CHAPTER V I
THE DEPOSITS LEFT BY THE GLACIAL ICE SHEET
37. The Graving Tools of Glaciers
The rocks embedded in the bottom layers of the ice could serve as graving tools only if held rigidly by the moving ice. It is known that ice free of rock has very little effect in moving over a smooth surface. Moreover, wet or warm ice does not hold rock firmly, but tends to permit it to rotate readily where in contact with the underlying surface. Rock is held rigidly only where the surrounding ice is cold and dry. Hence the scoring or smoothing action of moving ice should be greater during winter and at some distance back from the melting ice front.
The bottom of the ice sheet is debris laden. It is liable to contain fragments of all the rock over which it has passed. By the slipping of rear layers of ice over those in front, in crossing some valley or descending [p. 89] some hill, the lower parts of an ice sheet usually become rock laden for some considerable distance above its base.
It is a curious anomaly that the lower parts of a glacier may become so filled with rock that it no longer serves well as a graver of the underlying rock surface. Owing to the great quantity of rock fragments in the
[Photo: Glacial boulders of Canadian granitic rocks}
ice, the relative quantity of the enclosing ice may be reduced to such an extent that it no longer serves as a good binding material, and therefore fails to hold the enclosed rock rigidly. The principle is about the same as using too much sand and gravel and too little cement in mixing up concrete. Hence the bottom of an ice sheet enclosing too great an amount of debris may do very little scoring of the underlying rock surface. This probably accounts for the fact that glacial scratches are not more commonly found on rock surfaces on removing the overlying debris. Sometimes glacial [p. 90]scratches are absent over wide areas where the character of the rock surface is favorable to their retention.
It is probable that in some cases the rock-laden bottom of the ice sheet was so loosely held that it was thrust forward but very little by the overlying ice sheet, the latter over-riding its debris-laden base, and, at times, passing even over sand and gravel deposits without greatly disturbing their stratification.
38. Boulder Clay or Till Produced by the Grinding Action of the Moving Ice Sheet
In the process of smoothing the underlying surfaces of the rock, the glaciers reduced much of the ground-off material to powder. This powder, together with the great quantity of angular rock fragments still remaining, was continually carried southward, enclosed in the ice, by the forward motion of the glacier. This powder forms the clay, blue or brown in color, which locally rests upon the upper surface of the smoothed-off rock. When moist, this clay locally becomes very sticky. It is difficult to dig through it with a pick. The pick penetrates only a short distance and then is liable to stick so that it can not be pulled out readily. Hence the clay often is known as hard-pan, especially among well diggers. The scientific name for the entire mixture of clay and broken rock is till. Till, in fact, is the proper name for any rock debris left behind by a melting glacier. Since this till usually contains numerous rock fragments, it is known also as boulder clay. When boulder clay becomes dry under the influence of sunlight, it frequently becomes very hard.
Boulder clay may be recognized, when in large masses, by the entire absence of arrangement in layers. The rocks occur irregularly distributed throughout the mass of clay. Large fragments are intermingled with small ones, and both are more or less angular in form. This angularity of the fragments and absence of arrangement in layers is due to the fact that the boulder clay was not deposited by water, but was transported by ice.
Originally, the bottom part of this till must have been more or less in contact with the underlying rock, at least along part of its course. The [p. 91] larger part of the till however, must have been more or less embedded in the lower part of the ice sheet. When the ice melted, the till dropped. Such enormous quantities of till were included in some parts of the ice that the till left behind formed a thick deposit or covering over the underlying rock.
The rocks within the till are the implements with which the moving glaciers ground the underlying rock surface. Frequently these rocks indicate their former use as grinding tools by being more or less smoothed and striated themselves. Frequently they present flattened surfaces indicating that the rock fragments had been held more or less rigidly for some time while being dragged by the ice over the underlying rock. Even those fragments which occur far above the base of the till deposit often show strong striation and flattening, showing that they once were included in the basal parts of the ice sheet, but were forced upward, probably by the sliding of different parts of the basal layers over each other, those from the rear sliding over those farther toward the front, locally. In this manner the till gradually worked its way farther up into the lower parts of the ice sheet, which evidently in some areas must have been heavily charged with till for a considerable distance above the base.
In a similar manner, the ice sheet, near its margin, often was pushed over sand and gravel layers, leaving till deposits far above the striated rock surfaces beneath, and separated from the latter by considerable thickness of water-transported materials. In fact, near the margins of the ice sheet, the till and sand or gravel may be more or less interbedded.
39. Till Deposits in the Vicinity of Dayton
Numerous till deposits occur in the vicinity of Dayton and some of these are of considerable thickness. They may be recognized by the abundance of clay, often very hard where exposed to the sun, usually enclosing angular fragments of rocks, irregularly distributed throughout the clay mass.
One of the best know deposits of till is that at the Pinnacles, about a mile northwest of Alexandersville, on the north side of the great bend in the Miami river. Here a vertical height of 80 feet of till is exposed. For- [p. 92]
[Photo: The Pinnacles, four miles southwest of Dayton, west of the Miami river, seen from the west. An enormous till deposit, formerly washed at its base by the Miami river, but protected for many years by the embankment followed by the C. H. and D. railroad. The imponded waters back of the embankment are shown on the right. The exposed surface of till has been strongly gullied and ridged. In the immediate foreground one of the ridges ends in a tall wedge-shaped mass. A short distance farther back another ridge ends in a sharply pointed pinnacle. Photographed in 1895.]
merly this till was deeply gullied by the wash of rains, and the intermediate parts were left as sharp ridges. Thirty years ago, the terminal parts of several of these ridges rose into acute peaks, which could be ascended only by straddling the sharp ridges at points farther back, and then gradually working forward toward the peak. At this time the name Pinnacles was a very appropriate term for this great till exposure. It was a favorite [p. 93] picnic resort, and an abundance of wild flowers could be secured in the lowland surrounding the pond, and in the narrow valleys among the surrounding hills. This is the only locality near Dayton where the yellow blossoms of the witchhazel may be found in October, after the leaves begin to fall. It forms a large sized shrub or small tree, and its habit of beginning to blossom in the very late fall may be of very recent origin, as geologists reckon time, since the structure of the flower bud is that of a spring blossoming plant.
Northward from the Pinnacles, the till may be traced toward the Soldiers’ home. It underlies most of Dayton View. Since it is quite impervious to water, cellars filled with water after a heavy rain remain damp for a very long time, as many an inhabitant of this suburb, whose home is not connected with the city sewers, will admit. Till frequently is exposed here in digging foundations for buildings. Till forms most of the hill land west of Forest avenue, and it was struck within 6 feet of the road level in digging a sewer at the southern end of this avenue.
In digging the pits for the abutments of the Main Street bridge, this till formed the considerable thickness of “hard-pan” which the workmen found so difficult to remove.
South of the Pinnacles, till may be traced to Germantown. One mile east of Germantown, south of the great bend in the traction line, where Twin creek assumes a southerly course, the till deposits have a thickness of at least 70 feet, down to the level of the creek. These deposits have become quite famous since they include at the base a thin layer of peaty soil containing cedar berries, fragments of wood from some evergreen or coniferous tree, mosses, grasses and sedges, which must have lived before the advent of that part of the ice sheet which left the overlying till. These plant remains evidently are a remnant of a flora living thousands of years ago. In a similar deposit near Wilmington, Ohio, Doctor George M. Austin found the hard parts of beetles. In fact, sufficient plant and animal remains have been found in the glacial deposits in different parts of the world to give us some clue as to former climactic conditions. These were, of course, colder than those existing at the present day. [p. 94]
[Photo: Till deposit at the bend of Hole’s creek, north of the bridge on the Bellbrook road, two miles east of Alexandersville. This till deposit occurs west of the southern end of the Walden gravel ridge and formerly was connected across Hole’s creek with the great till deposits covering the hill fronts on the southern side of this creek.]
Another great till deposit is located along Hole’s creek, about 2 miles east of Alexandersville. It may be reached by following the western outline of the hills southward for a distance of about a mile from the Delco Dell. Here the northern margin of the creek is cutting at the base of a steep wash of the hill slope. Almost the entire exposed face of the hill consists of till. At a considerable distance above the creek, this till is overlaid by a continuation of those sands and gravels which, farther north, form the gravel ridges of Delco Dell and the Moraine farm.
It is probable that till underlies the entire gravel ridge area north of the Moraine farm as far as the bluffs at the Calvary cemetery and the hills east of Carrmonte.
At the gravel pit worked by the Washed Gravel and Sand Company, along the northwestern margin of the Calvary cemetery, till is exposed [p. 95] between 22 and 25 feet above the level of the canal, and appears to be abundant up to a level of 40 feet above the canal. It probably extends far below this level, but there is no exposure at present at any lower level in this vicinity.
Till, however, is not confined to any particular level. Since the glacial ice moved both up and down hill, there is a possibility of till occurring wherever the ice has been. Since the ice sheet in the vicinity of Dayton moved in a direction about S 30 degrees E, it is evident that, after crossing the Miami valley in the southwestern part of Dayton, it would push up against the hills on the southeastern side of this valley. In early geological times, before the gravel ridges in the area between Carrmonte, Hills and Dales, Moraine farm and Delco Dell had been formed, the eastern side of the Miami valley was formed not by the high land now stretching southward from Calvary cemetery to the Grand View farm, south of the Stroop farm and west of Delco Dell, but by the high territory extending north and south along the Lebanon pike, more than a mile east of the Delco Dell. Along this eastern margin of the ancient Miami valley, the advancing ice sheet plastered the hill slope with till, a part of this till rising considerably above the level of the till in the gravel pit northwest of the Calvary cemetery.
Nothing but till was struck in digging the cellar and boring the first well at the residence of Doctor Scheibenzuber, south of the Frederick farm, half a mile north of the Stroop road, on the western side of the Lebanon pike. The first well there was bored to a depth of 180 feet without striking anything but till. Nothing but till was struck in digging a trench southward from the residence toward the small stream at the foot of the hill slope. Westward, however, the overlying gravels come in. The structure, here, is that of a till sheet rising toward the ancient hill surface eastward, covered by a great mass of gravel and sand, thick westward, but thinning out eastward, on approaching this same hill surface. The top of the till at the Scheibenzuber residence attains an elevation of 1,000 feet above sea level, while at the gravel pit northwest of the Calvary cemetery the top of the main mass of till is only about 780 feet above sea level, but even the [p. 96] latter is far above the rock floor underlying the sands and gravels now filling the river valley.
Till underlies most of the hill surface east of the Lebanon pike, as far north as Beavertown and thence toward Huffman hill.
At the quarries northeast of Beavertown, now abandoned, the following observations were made by Frank Leverett, about 15 years ago.
“A good exposure of the structure of nearly plane-surfaced upland drift appears at the Beavertown quarries 3 to 4 miles southeast of Dayton. There is being removed here about 20 feet of drift, consisting of an almost continuous capping of yellow till 5 to 10 feet in thickness, beneath which are deposits of poorly assorted gravel and sand horizontally bedded. In places these gravelly deposits reach to the (underlying Dayton) limestone, but fully as often a thin bed of till intervenes. The surface of this lower till is uneven, and the gravel rests unconformably upon it. The lower beds of gravel being horizontal, are shut off where the till rises above their level. This break between the lower till and the overlying deposits may indicate a lapse of considerable time between their deposition, though it is not known but that the erosion of the surface of the lower till was rapidly accomplished by the same streams which deposited the overlying gravel and sand.”
Thirty years ago I was much interested in digging out of this lower till deposit fragments of wood, often two inches in diameter and 12 to 1 inches long. The wood came out of the till in good condition, but, on drying, it cracked considerably, especially lengthwise, and separated also into layers, parallel to the rings of growth. This wood evidently consisted of remnants of some coniferous or evergreen tree. At that time we were in the habit of calling them cedar, but no microscopical examination of the wood was ever made, and hence their exact identity can not be considered as established. They may have been fragments of tamarac or of some other coniferous tree. Possibly they were obtained from trees growing not far north of Dayton, since during the ice age many plants must have existed at Dayton which under present conditions would not be expected south of Ontario. [p.97]
Another instance of till plastered against a hill front on the eastern side of the Miami valley is shown in the northeastern part of Ohmer Park. Here a small country schoolhouse has been located for many years about two squares east of the corner of Wyoming and Arbor streets. Several squares north of this school, near the western prolongation of Alice street, and within easy reach from the Wyoming street car line, a gravel pit, 35 feet deep, is located. It is on the western side of a narrow valley. This valley formerly was ascended by the mule railroad, extending from central Dayton southeastward to the now long abandoned Dayton limestone quarry along the Smithville road. The right of way for this railroad passed north of the schoolhouse already mentioned, and still may be traced back toward Dayton as far westward as the northward prolongation lf Carlisle street, about half way between Tacoma and Wyoming streets.
The gravel pit, south of the schoolhouse, is run by Paul Nill and C. H. Delaplane. Its base rests upon the top of a great sheet of till. At this locality the till consists of blue clay, almost free from rock. It evidently was deposited under peculiar conditions, since the clay tends to crack horizontally, as though deposited under the influence of water action. Southeast of the gravel pit, up a narrow gully, the blue clay rises to higher levels than at the bottom of the gravel pit, as though plasterec against the hillside southeastward.
Till probably underlies a great part of the territory in the vicinity of Dayton, even where it is not exposed. In the territory covered by the gravel ridges, south of Dayton, its presence is concealed by the covering of sand and gravel.
39A. The Well at Delco Dell
In 1913 a well was drilled by Ira W. Barnes on the side of the hill at Delco Dell.
Beginning at the surface of the earth the well passed in succession through two feet of loam, 10 feet of clay, 15 feet of gravel, 50 feet of fine sand, 90 feet of hard-pan, 2 feet of gravel, 15 feet of clay, some kind of blue rock 2 feet in thickness, 14 feet of dark blue clay, and finally 37 feet [p.98] of clay which was a real dark purple, with some shale, toward the top and which changed to a light pea green below. The total depth of the well was 237 feet.
The expression hard-pan, used by the well-driller, almost invariably means till. According to this observation 77 feet of soil, gravel, and sand here overlie a great thickness of till deposits. The fragments of rock shown me from the 184-foot level consisted of glaciated pebbles from a till deposit. The till deposit evidently was continuous from the 77-foot level down to the 200-foot level below the top of the well. This gives an estimate of at least 123 feet for the thickness of the till penetrated by the well. It is not worth while attempting to determine the character of the light pea green clay material, without seeing a sample. It may still belong to the till section. If it formed part of the basal Richmond or upper Maysville section of rocks there should have been evidence of the presence of some limestone, though only in comparatively thin courses. The apparent absence of such limestone fragments suggests that at the bottom of the well the boring was still in the till, the underlying rock not having been reached.
It is quite evident that it is useless to search in this immediate area for water below any level which is on a horizontal line with this level of 77 feet below the top of the Barnes well at Delco Dell. Till is never a water carrier, although immediately above the till water may be expected in abundance locally.
Eastward, toward the Doctor Schiebenzuber farm, the level of the top of the till evidently rises, although probably in a very irregular manner. Westward the top may descend to still lower levels.
40. The Material Carried Forward Within the Ice Sheet Forms the Ground
The material carried forward by a glacier and left behind after the melting of the ice forms the moraine. In mountainous areas a large part of this material may consist of rock dislodged from the overhanging cliffs and may be carried on top of the ice. Tyndall describes in a very interesting manner the continual rain of rocks falling from the mountain heights [p. 99]
[Photo: Pebbles eight to twelve inches in diameter exposed by the removal of the soil following the deforesting of the land, on the western slope of the Pike ridge, just south of the Sub-power station, south of the O’Neil road. Photographed by Prof. J. L. Lambert. Any attempt to farm this land soon results in the removal of the soil. This land is suitable only for forestry or grazing.] [p. 100]
on the upper surface of a glacier whose rate of flow he desired to measure. So numerous were the fragments that the surveyor at times found difficulty in keeping his instrument in position long enough to accomplish his work.
In the case of continental ice sheets very little rock could have been carried on the surface, and that only within comparatively short distance from the cliffs from which they fell. Sooner or later these fragments of rock drop from the surface into the crevices which open where the ice changes its direction of flow or drops to some lower level or passes over an obstruction. At some point farther on, the pressure of the ice shoving from behind may close the crevices again, and then any rock which has fallen into a crevice not extending down to the bottom of the ice sheet becomes englacial, or is embedded in the ice.
Evidently most rock carried along by a continental ice sheet must be embedded within its basal parts, having been picked up by ice from the underlying rock over which the ice sheet passes. Owing to the sliding of the basal layers of the ice sheet over each other the lower part of the sheet becomes charged with rock for a considerable distance above its base. Sometimes this rock is so abundant, especially near the end and at the sides of a glacier, that it is difficult to determine where to draw the line between the bottom of the glacier and the underlying deposit of more or less loose rock fragments.
That part of the moraine which was carried along chiefly embedded within the lower part of the ice sheet, and which was left behind by the melting of the ice sheet, forms the ground moraine. At any considerable distance back from the ice front this ground moraine consists chiefly of broken rock and clay – the mixture called till. Nearer the margin of the ice sheet, the melting waters might give rise to streams running along channels underneath the ice, and these might wash away the clay and round the rock fragments into gravel and sand.
The melting of the ice sheet at its margin not only releases the rock embedded within its lower parts, but also allows the englacial rock, far above its base, to drop, and this rests upon the ground moraine or is embedded within its upper part. Since this englacial rock has suffered little [p. 101] wear since falling on the ice, it is likely to consist in part of large and only moderately rounded boulders.
41. The Shifting of the Front of the Ice Sheet
A continental glacier moving southward sooner or later must reach a climate sufficiently warm to cause the ice to melt. Melting, of course, tends to decrease the distance to which the ice may spread from the center of dispersion.
If the rate at which the ice melts back at its front margin exactly equals the rate at which the ice itself moves forward, the front of the ice sheet appears stationary. If melting takes places at a more rapid rate, the front of the ice sheet appears to retreat. If less rapidly, the front of the ice sheet advances. Evidently, under all three conditions, whether the front of the ice appears to be stationary, retreating, or advancing, the ice itself actually is moving forward.
All three conditions may exist during the same year, but at different seasons. In summer, the front may be retreating. In winter, it may be advancing, and during parts of spring and fall it may be stationary. However, it is chiefly the accumulated effects of all the changes during a series of years which prove interesting. A preponderance of forward motions during a number of years might result in the ice front moving forward a distance of several miles; or a corresponding series of apparent backward motions might result in a considerable retreat of the ice front.
Changes of this kind suggest a change of climatic conditions, such as often are discussed by the weatherwise. In reality, however, supposed climatic changes usually tend to balance each other. A series of warmer years usually is followed by a corresponding series of colder years, the general average for a long period of years remaining the same, so that it is not safe to assume that any more permanent change of weather conditions has taken place unless the records cover many years. Similar changes of climate, but on a larger scale, unquestionably took place during the long lapse of time covered by the so-called glacial period. [p. 102]
42. The Terminal Moraine
The ice sheet, of course, could not carry the rock embedded within it farther forward than the ice itself moved. This is so obvious that it requires no further comment. But what became of the embedded rock and clay? Naturally, it would remain at the most southern point to which it had been carried before the ice melted, unless moved still farther onward by some stream or other agency.
It is evident that if the ice sheet, in moving southward, for a period of many years reached approximately the same point before its advance was halted by melting,- in other words, if the ice front remained approximately stationary, - a great quantity of rock and clay would accumulate along its margin. This accumulation would include not only the till embedded within the lower part of the glacial ice, but also any englacial or superglacial rock carried along by the middle or upper parts of the ice sheet. Such an accumulation of till and englacial rock along the front margin of a glacier is known as a terminal moraine.
Terminal moraines at the bottom of glaciers occupying narrow valleys sometimes are so distinctly defined that they appear almost like transverse ridges halting the further advance of the ice. Such distinctly defined terminal moraines are exceptional and probably mark accumulations of no great number of years at the base of glaciers charged to an unusual degree with rock fragments and rock powder and clay.
The terminal moraines of the ancient continental glacial ice sheets rarely are so distinctly defined. Frequently they spread over a width of two miles and rise only from 40 to 80 feet above the general surface of the land. Such a low and broad elevation, especially where the upper surface is irregular, can not be recognized by the average observer as a ridge, and hence must be identified by the student who recognizes the morainal character of the deposit by means of the material of which it is composed and by carefully mapping its distribution with reference to other deposits.
It is evident that, compared with the moraines of Alpine valleys, the terminal moraines of continental glaciers must represent much slower rates of accumulation of rock and clay, due to the much slower rates of motion of [p. 103] the glacial ice over much flatter territories. During the much longer periods of accumulation the ice front probably shifted forward and backward repeatedly, frequently over-riding earlier accumulations and smoothing out steep slopes by addition or removal of material, so that the average topography of the terminal moraine of a continental glacier is not sharply defined.
43. The Melting of the Ice Sheet
The melting of the ice sheet, of course, was not confined to the margin of the ice sheet. Glacial climate probably was only moderately colder than our present climate. It has been estimated that a lowering of the average annual temperature less than ten degrees would be sufficient to account for the former widespread glacial conditions. Apparently the colder climatic zones of the earth had shifted southward, toward the equator, but there is no evidence of excessive low temperatures. During the warm season of the year the ice must have been melting everywhere, even at its centers of distribution. Under the influence of the sun, melting must have taken place over wide areas also in winter.
Attention has been called already to the streams issuing from beneath the margins of glaciers even during the coldest days in winter. Evidently the lower parts of the ice sheet melt continually, owing to the pressure of the enormous amounts of overlying ice.
Evaporation probably also played an important part in the thinning of the ice sheet as it progressed southward. Even in the solid state ice evaporates considerably as is shown by wet clothing hung out to dry in freezing weather, and evaporation must have been rapid in warmer weather when the upper layers of the ice were soggy with water.
The most rapid melting, of course, must have taken place near the margin of the ice sheet. Here enormous quantities of water must have been released, forming many streams carrying rock, sand, and mud forward from the ice front.
44. Subglacial Streams and the Formation of Eskers
Sooner or later the water formed at the surface of the ice sheet, by melting, finds its way into crevices, and either is absorbed by the ice or [p. 104] finds its way down to the lowest depths, where it joins the water produced by the melting of the basal parts of the ice, owing to pressure, as explained in the preceding lines. These may be called the subglacial waters or those which exist beneath the ice sheet. They frequently flow along distinct channels, and form subglacial streams. Where they issue from beneath the ice sheet, at its margin, they may be of large size, as is the case of the Rhone, which is already a stream of considerable size where it appears from beneath the Rhone glacier.
[Drawing 1: Diagram representing gravel and sand deposits left by a sub-glacial stream. The deposits, of course, are much more irregular than here indicated. The top of the glacial ice must be imagined as far above the highest part represented in the diagram.]
[Drawing 2: A gravel ridge or esker formed by the slumping of the upper part of the gravel and sand deposit, after the melting of the ice. In this diagram the slumped part of the deposits are shown as having lost all evidence of bedding or arrangement in more or less distinct layers. In nature, part of the slumped material might retain evidences of former bedding.]
Where subglacial streams flowed along confined channels, the waters must have flowed with great velocity. Such streams must have been charged heavily with rock and sand and mud from the melting base of the glacier, and the rock fragments must have been rounded and more or less sorted into layers, as in the case of ordinary streams, not flowing beneath glacial ice.
Where the subglacial streams occupied narrow channels, supported on the sides by steep walls of ice, the accumulations of gravel and sand along the stream channel may have been of moderate width compared with their total thickness. However, after the melting away of the lateral supporting walls, on the disappearance of the ice sheet, the lateral edges of the sand and gravel layers must have slumped off and rolled down, adding to the width of the deposit at its base, but permitting its top to become much narrower and more ridge like. In this manner, a deposit 100 feet wide at the top and 100 feet high might narrow to a width of 25 to 30 feet at the [p. 105] top and widen to more than 170 feet at the bottom. Such slumping could be detected best by a cross-section of the glacial stream deposit. The material which had rolled down the slope of the ridge toward its base would not be arranged in layers, but would lie in disorder against the lateral margins of those more central parts which still preserved evidence of arrangement in layers under the sorting action of running water.
Such narrow ridges of sand and gravel deposited by subglacial streams are known as eskers. They represent narrow stream deposits originally supported laterally by walls of ice. Eskers are phenomena chiefly of the extreme front of the ice sheet. Usually they are less than a mile long, but eskers scores of miles in length are known.
The long narrow gravel ridges south of Dayton extending from Calvary cemetery and Carrmonte southward to Moraine farm and Delco Dell, are eskers.
45. The Gravel Ridges South of Dayton Represent Stream Courses Beneath
the Ice Sheet
From this point of view, the long narrow gravel ridges south of Dayton may be regarded as marking the location of former subglacial stream courses, or rather, of such parts of former stream courses as still are preserved. The subglacial streams, in general, flowed southward. Sometimes adjacent stream courses united, as in the case of the Nollman and Pike ridges, west of the Cincinnati pike. Here the depression crossed by the Nollman lane may be due to the increased swiftness of the waters at the point of junction of the streams. In the Hills and Dales, the Adirondack, Panorama and Watershed ridges unite near Inspiration point, in a region of high land in which the gravel and sand deposits form an almost continuous sheet.
46. Gravel Ridges Formed During Closing Stages of the Glacial Ice Age
Frequently the subglacial stream courses were united by short transverse channels. West of the Cincinnati pike, the Chapel and Pike ridges [p. 106] are united by the Nollman and Peters ridges. The Eastview and Sunset ridges are united at several points by short transverse ridges, the most conspicuous of which is at the Tip Top knob, at the southern end of the Old Orchard hollow, on the Moraine farm. Connecting ridges are seen also in the Delco Dell area. One of these is followed by the main road entering the grounds. It is probable that the spurs projecting westward from the Delco ridge, in the Delco Dell area, represent similar transverse channels connecting with a north and south ridge farther westward, of which only partial remnants remain. Short lateral spurs occur also on the western side of the Sunset ridge, northwest of the Summer camp, on the Moraine farm. Larger spurs on the Grand View Hill farm, southwest of the Delco Dell area.
The presence of these transverse ridges and short spurs suggests that the front of the ice sheet must have been very stagnant at the time of their formation. Moving ice would have shifted these lateral channels and would have spread their deposits over a wider territory. The ridge-like character of the deposits in these transverse channels would have been largely obscured.
Moving ice probably would have obscured also the sharpness of definition of the main gravel ridges, such as the narrow parts of the Pike and Chapel ridges, west of the Cincinnati pike, the northern part of the Adirondack ridge in the Delco Dell area, and the best defined parts of the ridges on the Moraine farm and in the Delco Dell area.
It is probable that the gravel ridges were formed during the closing stages of glacial action in this part of Ohio, when the ice front was melting back. There is no evidence that the ice sheet ever extended so far southward again. The deposition of the sands and gravels may have taken place in a very short time. Given an abundance of water and rapidly flowing streams, and a few years would account for all the gravel ridges seen south of Dayton. Under favorable conditions even a few months might suffice. At any rate, the formation of the gravel ridges probably was but a brief and minor episode in the long-continued glacial history of our continent.
Possibly the rapidity of accumulation of the gravel ridges accounts in part for the great variation in the heights attained at different points along [p. 107]
[Photo: View of Cornfield hollow, looking north. This hollow lies west of the Lohman ridge. This is an excellent illustration of the frequent occurrence of low depressed areas, without drainage outlets, between the parallel gravel ridges.]
their crests. Deposition, in general, is an evidence of arrested, or at least, diminished transporting power. At the most rapid points of flow, the sand and gravel would be carried off; at the less rapid points they might remain. It is the points of more rapid flow that give rise to the swimming pools along streams.
47. The Kame Area
Streams flowed not only along channels beneath the ice, but at the margin of the ice sheet, also in the re-entrant angles of the ice margin, and over the areas immediately in front of the ice sheet. Here, where the waters could spread over the flat lands, the violence of their rush was much diminished, and thick deposits of gravel and sand were formed. The irregular accumulation of these materials, accompanied by the irregular advance and recession of the ice front, produced a very irregular land surface, including hills, knobs, ridges, long hollows, and irregular depressions, known as kame moraines. The term kame is most appropriate for the knob, hill, or ridge [p. 108] built up by running water resulting from melting glacial ice, but it may be used also for those accumulations of stratified sand and gravel in which the topography is scarcely pronounced enough to result in well defined hills and hollows.
North of the O’Neil road, the kame territory extends at different points from more than half a mile to nearly a mile west from the Cincinnati pike. In the Hills and Dales area it includes all of the country east of the Wayne’s Pass road, as far south as the Locust farm, and the Stroop road. South of Delco Dell and the Grand View farm, the kame area extends as far as Hole’s creek. The gravel ridges are merely the most striking topographical features of the kame area.
48. The Outwash Plains in Front of the Glacial Ice Sheet
Kames, in general, are hill-like accumulations of sand and gravel near the margins of the ice sheet. Where glacial streams, at the margin of the ice, entered large, flat valleys, with only a moderate slope, their rate of flow must have diminished rapidly, resulting in large accumulations of gravel and sand, raising the level of the stream channel and causing overflows, resulting in a continual change in the paths of the stream channels. At a greater distance from the ice front, these streams must have carried chiefly sand and mud, forming immense sand plains and mud flats, such as the large flat lands extending from Dayton down the Miami valley as far as West Carrollton and Miamisburg. The large flat country west of the bluffs, and extending east of the Cincinnati pike as far as the western edge of the hill country on the Moraine farm, is a large outwash plain. Opposite the Moraine farm it has a width of fully two miles. The Huffman prairie area, extending from the Wright Aviation field, several miles northeast of Dayton, toward Fairfield and Osborne, is another outwash plain of large dimensions. [p.109]
[Photo: View from the ridge southeast of the Emrick farm buildings across the flat lands of the Miami valley. The farmhouses are located west of one of the conspicuous gaps across the northern extension of the Walden ridge. The gap in the immediate foreground, occupied by the buildings, is through the Emrick ridge, one of the frequently interrupted ridges.] [p. 110]
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