DIRECTION OF FLOW OF THE STREAMS PRODUCING THE GRAVEL RIDGES
17. Direction of Flow of the Streams Producing the Gravel Ridges
The direction of flow of the streams producing the gravel ridges may be determined much more readily than might be imagined by those not familiar with the method of conducting such researches. The procedure is simple.
South of Dayton, the streams producing the gravel ridges must have flowed either north or south, in the direction indicated by the ridges.
If the pebbles forming the ridges are merely fragments of rock which have become rounded since they were broken off from their original ledges, their origin might be ascertained in certain cases merely by determining from what kinds of rocks the pebbles have been formed, and where rocks of [p.53] this kind still are to be found in their original form as layers or ledges. Should any of these rocks prove sufficiently peculiar to be identified readily, and should the distribution of the layers or ledges from which they could have been derived be such as to indicate only one possible direction for the source of the rock, then the problem would be solved.
By such methods it has been determined that many of the pebbles found in the gravel ridges could have come only from the north. Hence the streams transporting these pebbles also must have come from the north, and the associated pebbles, whose origin could not be determined so readily, evidently must have been conveyed by the same currents, from the same direction.
18. The Rocks of Western Ohio and the Adjacent Parts of Indiana
The method of determining the origin of the pebbles in the gravel ridges near Dayton will be understood more readily if the character and distribution of the rocks found in Ohio, Indiana, and that part of Canada which lies immediately north of these states be known. For that reason the following brief statement of the character and distribution of these rocks is added:
If you were to visit the gorge of the Whitewater river, at Richmond, in Indiana, you would notice a great mass of comparatively thin limestones, arranged in horizontal layers, often interbedded with more or less clay, the entire series being known among geologists as the Richmond beds. Both limestones and clays are richly fossiliferous. Many of the most interesting fossils known to geologists have been discovered in this gorge. The same strata are exposed where the Springfield traction line crosses the railroad at the northern end of Huffman hill, east of Dayton. Excellent exposures of Richmond beds, at a lower level, occur along Hole’s creek, southeast of Moraine park, and, at still lower levels, in the big railroad cut along the Big Four railroad south of Miamisburg. The largest Indian mound in the United States is located on the hill summit, southeast of this railroad cut.
At the north end of the Huffman hill, east of Dayton, at a higher elevation than the exposures at Richmond, is found a massive layer of limestone, with a different texture and color, and containing a different group [p.54] of fossils. This rock has been quarried for many years at Centerville, in the southern part of the county, and still is used extensively in the construction of the numerous pikes in Montgomery and neighboring counties. It formerly was well exposed in the abandoned quarry at the Soldiers’ Home. For many years it was regarded as identical with the limestones known as Clinton, in New York, but at present the name Brassfield limestone is regarded as more appropriate. Its thickness varies from 18 feet near Dayton to about 30 feet northward, at Piqua. Recently the Brassfield limestone has become important economically on account of its large content of lime and its small content of magnesia. An area southeast of Tippecanoe City, near West Charleston, has been selected as the location for a large cement plant. The glacial clay deposit overlying the Brassfield limestone furnishes the necessary silica and alumina.
Overlying the Brassfield limestone is a very white and dense limestone, usually with very few fossils, formerly abundantly quarried in the vicinity of Dayton, and extensively used for window sills, porch flagging, sidewalks, and gutter stone. The courthouse, and several of the churches on Ludlow street, in Dayton, were constructed of this stone. The upper part of the quarry at Centerville furnishes an abundance of this solid white stone.
Numerous quarries formerly existed southeast of Dayton, along the Smithville road, also south of the asylum grounds, and in the vicinity of Beavertown.
The first railroad at Dayton ran from the central part of the city diagonally, southeastward, across the commons to the quarries, which at that time existed along the Smithville road, northeast of the Ohmer Park plat. Some parts of the old right-of-way of this railroad may be traced still in the woods, near the former quarries, and only a few years ago the old railway embankment could be followed from these woods for more than a half a mile northwestward, toward Dayton. Under the name of Dayton limestone this rock was transported to distant localities, and was at one time extensively used in the construction of buildings, the white color of the Dayton stone producing a pleasing contrast with the red color of the brick. The Dayton limestone is overlaid by a series of limestones and clayey shales called the Osgood bed, after a locality in Indiana. [p.55]
[Photo: Lower part of the Liberty division of the Richmond formation as exposed on Hole’s creek south of the Bellbrook road, about three and a half miles southeast of Alexandersville. The Hebertella insculpta horizon occurs at the base of these exposures. See figure 11 on the plates of fossils, page 208, and the various vertical sections across the preglacial valley of the Miami river. This is a good locality for collecting fossils. Note the small bend in the rocks. When these bends take place on a vastly larger scale they give rise to mountains.] [p.56]
On the way to Springfield, from the windows of the railroad train, cliffs of massive rock may be seen which belong at a higher level than the Osgood bed. The basal part of this massive rock, from 6 to 8 feet in thickness, is rather porous and is valuable only for crushed rock. The immediately overlying part is much more dense; it is comparatively even bedded and is quarried for building purposes. Compared with the Dayton limestone it is softer and has a more yellowish tint. The same rock is exposed at several quarries north of the Eaton pike, between Kingsville and the Union pike, about 3 miles west of Dayton. Here its thickness is 8 feet. The building rock contains an abundance of a peculiar large shell called Pentamerus oblongus, and is known as the Springfield limestone. The Springfield limestone contains too large a content of silica and alumina to burn into a valuable limestone.
The upper part of the rock at the Springfield quarries consists of a much more massive limestone, not at all suitable for a building stone, but very useful for quicklime. In the vicinity of Cedarville, this is the only stone exposed in the quarries and hence it is called the Cedarville stone. Numerous lime kilns have been constructed where this stone is exposed. The Shoup lime kiln, 6 miles north of Dayton, on the Troy pike, east of the Miami river, still is in operation. Lime kilns formerly existed also west of Dayton, at the localities north of the Eaton pike, already mentioned. In Canada, rock corresponding to the Cedarville limestone is known as the Guelph. The Cedarville limestone is one of the three most valuable limestones utilized in Ohio for the manufacture of lime. It is an almost pure carbonate of lime and magnesia, with very little silica or alumina.
At the southern point of Put-in-Bay island there is exposed a considerable thickness of limestone, some of which is very thin bedded or laminated. This is a part of the Monroe limestone which underlies a greater part of the state of Ohio than any other large division of rock excepting the coal measures of the eastern part of the state. This limestone extends southward as far as Wapakoneta, St. Paris, Urbana, London, Washington Courthouse, and Vanceburg on the Ohio river.
In the large quarries visible from the railroad train just before enter- [p.57]
[Photo: Lower part of the Cedarville limestone at the Shoup Lime Company quarry, on the old Troy pike, seven miles north of the center of Dayton. The top of the Springfield limestone forms the floor of the quarry.]
ing Columbus, the Columbus or Onondaga limestone is exposed. Certain layers of this limestone contain numerous fish teeth and other fish remains. This limestone extends northward to Kelley’s island, east of Put-in-Bay, and exposures are found also in Michigan and southern Ontario.
Above the Columbus limestone occurs a clayey limestone, more or less interbedded with shaly clay layers, often containing numerous shells and other remains of former marine life, readily weathering out of the clay. This limestone is exposed in various parts of Michigan and in that part of Ontario which lies between the southern end of Lake Huron and Lake Erie. It extends also southward through central Ohio to Delaware and Columbus. It is known as the Delaware limestone.
Proceeding southward from Dayton, along the valley of the Miami river, the series of thin limestones and clays, known as the Richmond group [p.58]
[Map: Geological map of Montgomery and adjacent counties. The white part is underlaid by strata ranging from the Cedarville down to the Brassfield limestone. The light shaded part is underlaid by the upper half of the Richmond group of rocks, including the Elkhorn, Whitewater and Liberty. The darkly dotted part is underlaid by the lower half of the Richmond group, including the Waynesville and Arnheim. The darkly lined part, south of Miamisburg, is underlaid by the top of the Maysville group of rocks.] [p.59]
of rocks, continues to be exposed as far south as Miamisburg. From the vicinity of Franklin to beyond Hamilton, a lower series of thin limestones and clays, known as the Maysville group, from a locality in Kentucky, is exposed. At a still lower level, from below Hamilton to near low water in the Ohio river at Cincinnati, a third series of limestones and shales, known as the Eden group, from Eden Park, in Cincinnati, is present.
If now the names of the various limestones here mentioned be arranged in a vertical column, the name of the rock belonging lowest in the series being placed at the bottom, and the names of the overlying rocks being placed successively nearer the top, the following list would result:
Osgood limestone and clay shale
Richmond group of limestone and clay
Maysville group of limestone and clay
Eden group of limestone and clay
In this form the list might be called a list of the rocks of western Ohio, eastern Indiana, southern Michigan, and southern Ontario. It is not a complete list, nor is it such a list as would be published by geologists. While most of these names apply only to minor divisions of rocks, the so-called groups include series of strata whose total thickness is vastly greater. Nevertheless, this list will serve to designate some of the rocks of interest in determining the origin of the pebbles in the gravel ridges, south of Dayton.
19. Differences Between Rocks Belonging to Different Groups or Subdivisions
On becoming sufficiently familiar with the different limestones named in the preceding list, it will be noticed that all differ more or less in their [p.60] density, porosity, and hardness, and in the coarseness of their grain. Some of the limestones are well bedded, or separate readily into horizontal layers from a few inches to a foot or more in thickness. In other rocks the bedding is very irregular, or the rock may not separate readily into layers. In the latter case the rock may be called massive. In some rocks, even the individual layers are seen to be made up of many very thin sheets, which, however, do not separate readily from one another, but remain firmly attached so as to form a single, sold layer, several inches thick. Different limestones differ more or less in color. They differ often considerably in chemical composition, and although this difference may not be recognized readily by the average observer, the limekiln operator soon learns that there are differences. Some rocks are more suitable for lime than others. Some produce quick setting limes, other produce limes that set more slowly. There are differences even in the layers of the same quarry.
20. Different Fossils Found in Different Groups of Rocks
There are differences also in the fossils found in different layers of rock. Each of the limestones here listed is characterized by a different group of fossils.
It is taken for granted that the reader knows that fossils are merely the remains of former living animals, consisting usually of the hard parts, such as shells and bones, which have resisted decay. The term fossil may be uses also to indicate impression of these hard parts and is liable to be used for almost any evidence of the former presence of life if sufficiently distinct to suggest the nature of the animal.
As a rule, it does not require a profound knowledge of fossils to be able to recognize the differences in the fossils found in different layers. The average student of geology at college does not spend 50 hours in the study of fossils, and the knowledge acquired in this short time can scarcely be called profound. Usually only a slight acquaintance with fossils is necessary to determine to what subdivision any exposure of rocks belongs, provided that the fossils occur in the rock in sufficient abundance. But it might require more expert knowledge to identify any rock with confidence [p. 61] if the enclosed fossils are both rare and poorly preserved. However, it would astonish most persons not familiar with such studies to observe with what speed and confidence an expert geologist, already familiar with the characteristic fossils of the different limestones can identify the latter provided that the rock be supplied fairly well with fossil remains.
21. How to Determine From What Subdivisions of Rocks Certain Pebbles Were Derived
It is quite evident that frequently it must be quite easy to determine the subdivision of limestone from which a certain pebble was derived.
For instance, pebbles derived originally from the breaking up and rounding of fragments of Clinton limestone are likely to break rather readily under the blows of a hammer. The grain is coarse and crystalline. The rock usually does not show distinct bedding. The color is salmon brown, pinkish, or gray.
Pebbles derived from Dayton limestone are likely to be hard, very fine grained, and remarkably white.
Some of the pebbles derived from the Monroe limestone are fine grained, very hard, and show that the rock is made up of numerous very thin layers, which, however, do not separate from one another readily. The color may be light blue or dove colored.
The sources of some of the pebbles may be recognized by means of the fossils which they contain. Frequently when pebbles are broken up, they are found to contain fossils which can be identified readily, and if these fossils are confined to only one or two of the various subdivisions of rocks, the source of the rock forming the pebble usually may be determined readily, the character of the rock making up the pebble assisting greatly in this identification.
For instance, the presence of the large shell, Pentamerus oblongus (Figure 15, on page 208), previously named, if occurring in a fairly dense, fine grained limestone of a yellowish tint suggests the Springfield limestone as the source of the pebble.
Occasionally fossils may be found entirely free of the surrounding [p. 62] rock. For instance, Spirifir pennatus repeatedly has been found in the vicinity of Dayton, in gravels and other loose deposits. It is a characteristic fossil of the Hamilton formation, the approximate equivalent of the Delaware limestone, and its source may be determined as having been that of some Hamilton rock, even if no part of the rock formerly surrounding the fossil remains attached to the latter.
22. The Source of the Limestone Pebbles Found in the Gravel Ridges South of Dayton
On investigating the pebbles found in the gravel ridges south of Dayton, no specimens which could have been derived from the Eden or Maysville limestones, in the southwestern part of Ohio, south of Miamisburg and Franklin, were noticed. This suggests that the currents of water producing these ridges did not flow from south to north.
On the contrary, pebbles of each kind of rock found north of Dayton, from the Richmond limestone to the Delaware marly limestone, were found. Evidently the currents flowed from north to south.
Certain among these limestones are much more frequently represented among these pebbles than others.
Pebbles of Richmond limestone are abundantly represented and are easily recognized, usually being very fossiliferous. They form fully 14 per cent of the total number of the larger sized pebbles, 4 inches or more in diameter. The great quantity of pebbles from the Richmond limestone is explained by the fact that the rock occurs in thin layers, readily broken off; it is abundantly represented immediately north of Dayton, and the rock fragments were transported such short distances that they were not much ground up during transportation.
Fragments of Brassfield or so-called Clinton limestone are not common, but form only a small percentage of the total number of pebbles in the gravel ridges. North of Dayton this limestone forms massive cliffs not readily broken up, and the area within which this rock reaches the surface is comparatively small. Hence the probability of discovering pebbles from this source is small.
Similar statements might be made regarding the Dayton limestone. [p. 63]
[Photo: The cut across the Pike ridge at the O’Neil road, looking southward. Notice the narrowness of the ridge along the top and the steepness of slope of the sides. The photograph was taken from too great a distance to show the horizontal bedding of the gravel and sand layers Some of the pebbles found at this locality contained fossils known to occur only in Columbus limestone. This limestone crops out also in Ontario, on the eastern side of Lake Huron, and this probably was the origin of the pebbles.]
The rock is hard and the area of exposure is comparatively small. Only an insignificant part of the pebbles in the gravel ridges consists of this rock.
By far the largest proportion of the limestone pebbles occurring in the gravel ridges consist of Springfield, Cedarville, and Monroe rock, with the Cedarville apparently largely predominating. These three limestones furnish about 70 per cent of the total number of pebbles 4 inches or more in diameter. Of course, these rocks are present in the form of continuous layers or ledges over wide areas north of Dayton.
Several pebbles of Columbus limestone, containing excellent fossils, easily recognized, were obtained along different parts of the gravel ridges [p.64] between the Calvary cemetery and Delco Dell. The original ledges which these Columbus limestone pebbles were obtained occurred either in the extreme northern part of the state or farther north, in Michigan and Ontario. The rock is rather soft and easily broken up. The area of exposure northward is not very great and the distance over which transportation took place was considerable. Hence not many pebbles of this rock are to be expected. Although the Columbus limestone is abundantly exposed near Columbus, Ohio, it is known that the direction of transportation of the rock toward Dayton was from the north, not from the east.
Evidently the very soft marly Delaware limestone was not well adapted for distant transportation, and only occasional pebbles of rock or free fossils from this source are found.
This leaves 16 per cent of the total number of larger sized pebbles in the gravel ridges south of Dayton not accounted for. This 16 per cent of the total number of pebbles does not consist of any of the limestones listed above, but is made up of the granitic and metamorphic rock materials, discussed on pages 71-74.
23. The Sandstones and Shales of Northwestern Ohio and Adjacent States
Western Ohio, eastern Indiana, southern Michigan, and southern Ontario are pre-eminently limestone countries. North of Dayton the various limestones are interbedded with very little clay or clay shale, and practically none of this softer clay or clay shale can be identified among the materials forming the gravel ridges south of Dayton.
In the northern part of Ohio a little sandstone is interbedded locally in the middle of the Monroe limestone, but no pebble of this sandstone have been recognized among the pebbles at Dayton. In fact, sandstone of any sort or derivation is exceedingly rare among these pebbles. Occasionally, a fragment of sandstone occurs which appears to have been derived from some northern equivalent of the Waverly sandstone, as exposed in various parts of the southern peninsula of Michigan.
Considerable Ohio black shale underlies various parts of northwestern [p.65] Ohio and adjacent Michigan, but none of this black shale appears among the pebbles at Dayton. It is entirely too soft to bear transportation for such a long distance.
In order of succession, the Ohio black shale belongs above the Delaware limestone and is overlaid by the Waverly sandstone.
23A. How Rocks Are Formed
Every one is familiar with the fact that when gravel or sand are mixed with cement or lime in the presence of water, the entire mixture finally becomes hard, like rock. In fact, it is rock. It is just as much rock as any found in nature. It differs merely in having been formed artificially. Ordinary rock, such as sandstone and limestone, also consists of sand or fossil fragments cemented together by natural cement or lime.
In the case of sandstone, the cemented fragments consist chiefly of small particles of quartz, and the cementing material may be either lime, silica, or some iron compound. In the strongly colored red or brown sandstones, such as those used for the construction of the church at the corner of Forest and Grand avenues, in Riverdale, the cementing material consists chiefly of iron compounds. In the case of the ordinary sandstones, lime frequently is the cementing material.
The process is simple. Water percolating through decaying vegetation or animal material absorbs carbon dioxid gas, and in the presence of this gas dissolves minute quantities of the limestone through which it passes. At greater depths, where the water is under greater pressure, the amount of limestone dissolved is greater. On coming to the surface, where the carbon dioxid gas escapes, all of this limestone can not be held in solution, and part of it is deposited. At some localities it is deposited in such large quantities on old sticks and leaves which may happen to lie around at the point of exit of the seeping water that these become encrusted with lime or are entirely covered by the same. In these cases, on breaking open the lime deposit, beautiful impressions of leaves of trees often are found. Excellent examples of such leaf impressions are found by breaking up the porous, reddish brown lime incrustations at the western end of the lake in the Glen at Yellow Springs. [p. 66]
[Photo: A thin sand layer consolidated into rock. In the bed of the brook running through the Dr. Scheibenzuber farm.]
[Photo: Thin layer of sand consolidated into rock and now forming the top of a little waterfall. In the bed of the brook running through the Dr. Scheibenzuber farm.] [p. 67]
Where this lime is deposited in the crevices between sand grains, the loose sand becomes converted locally into sandstone. Sometimes parts of gravel beds are converted locally into solid rock. Excellent examples of this occur around Dayton. Large masses of consolidated gravel deposits formerly were seen along the bluffs, west of the Jewish cemetery, northeast of Carrmonte. Interesting example are seen along the brook running southwest of the Dr. Scheibenzuber house toward Delco Dell. At one locality a thin sand bed has been consolidated into a hard sandstone, and along both branches of the brook this sandstone has given rise to a tiny waterfall.
Farther up stream, thicker layers of gravel have been consolidated into rock layers, the fragments of which have fallen down the hillside, toward the brook. In these consolidated fragments the original pebbles of the gravel may be recognized readily. Sometimes the consolidation of the gravel is not uniform and very irregular blocks result, often producing very picturesque effects.
At one locality along the western margin of the Mad River road, a little over half a mile south of the David church, the unconsolidated part of one of these cemented gravel layers has been washed away so as to leave a part of the cemented gravel layer behind in the form of a tiny rock bridge. Picture on page 149.
What causes the lime to be deposited in one layer of gravel without affecting to any great extent the layers of sand or gravel at lower or higher levels, of course, can not always be determined. Frequently the cemented layer is underlaid or overlaid by a more clayey layer through which the water does not percolate readily.
In the case of the coarser grained limestones formed at the bottom of the sea, the grains usually consist of fragments of shells or other marine organisms which have become rounded by the wash of the waves and consolidated by the infiltration, between the fragments, of mud impregnated with lime. In the course of ages this mud and lime harden into rock, binding the entire material together. In some limestones the mud element may form quite a considerable part of the consolidated rock. In other limestones even the infiltrated mud may be calcareous so that the limestone [p. 68]
[Photo: Several gravel boulders along the northern edge of the brook running through the Dr. Scheibenzuber farm.]
[Photo: Gravel boulder north of the brook through the Dr. Scheibenzuber farm. Large holes have been weathered into this boulder.] [p. 69]
may be quite pure. The coarser the original fragments of shells and other organisms, the coarser will appear the grain of the rock. In some limestones the original deposit must have consisted almost entirely of calcareous mud since no grain can be recognized excepting under the microscope.
From the preceding notes it will become evident that sandstones and limestones are formed by the cementing together of grains of sand or particles of shells or other calcareous materials, sometimes readily distinguishable and at other times too fine to be readily recognized as made up of individual particles.
People sometimes ask: Do stones grow? A man once removed a very large Canadian boulder at considerable expense because he was afraid that if it were used as the support of part of a foundation wall it might grow and eventually split the foundation wall. Others have said that they knew of specific instances of boulders in the fields which had grown within their lifetime. Of course, in this sense rocks never grow. It is not always possible to determine how such erroneous impressions originate. Perhaps in one case the soil was washed away by rains from some boulder and allowed more of the lower part of the rock to be exposed. In another case, a foundation wall may have settled more where resting upon gravel than where supported by a large boulder, thus giving the impression that the latter has grown. It often is easier to start an erroneous impression by inaccurate observations than to correct this impression after it has become more or less general.
23B. The Crume Sand Lime Brick Company
The use of lime as a binding material in the conversion of loose sand into solid rock is illustrated by the sand lime brick industry. The process may be seen at the Crume plant, southwest of Dayton. A picturesque walk through the woods leading westward from the southern gate in the fort at the Calvary cemetery leads directly to the plant. The path diverges toward the right from the main woodland road passing southward from the gate of the fort, the latter being at the edge of the woods southwest of the Calvary monument. An enormous sand pit has been opened by the [p. 70] company along the western edge of the bluffs. The sand is mixed with lime in definite proportions, and then the mixture is pressed by machinery into the form of bricks. The scarcely coherent bricks are then loaded on trucks and run into long iron cylinders about 6 feet in diameter. The cylinders are closed and steam is turned on. The lime is converted by the steam into slaked lime and this soon hardens, converting the comparatively loose sand into hard brick. The longer this brick is exposed to the air, the more it takes up carbon dioxid gas, gradually converting the binding material into carbonate lime or limestone. The brick company, in producing its brick, merely does in a short time what nature accomplishes on a much larger scale, but also in a vastly longer period of time, in converting loose material into sandstone or limestone.
24. Rocks Originating Far Below the Surface of the Earth
Limestone, beds of clay, shale, and sandstone are all rocks originating at the surface of the earth, usually as water deposits, and most frequently as deposits on the bottom of the ocean.
Volcanic rocks are those which in a melted form have flowed through openings or cracks in the overlying rocks until they have reached the surface, as lava. When this lava cools within the cracks without reaching the surface of the earth, it is called a dike rock, and when it melts its way in enormous masses upward through part of the overlying rocks and cools long before reaching the surface, it may be called a deep-seated rock. Granites are deep-seated rocks, exposed at the surface of the earth only where the originally overlying rocks have been removed by millions of years of weathering. Granites most commonly are grayish and reddish in color, but some of the deep-seated rocks, such as diorites and diabases, have so many dark colored minerals, such as biotite, hornblende, and augite, that the general color of the rock is dark green or blackish.
None of these rocks—lavas, dike rocks, or granitic rocks—occur in Ohio, Indiana, or in the adjacent parts of Michigan or Ontario except as fragments brought in by some agency from ledges occurring in some more northern areas. Nevertheless, representatives of these rocks occur among the pebbles in the gravel ridges south of Dayton, forming about 10 per cent [p. 71] of the larger pebbles, meaning by this those pebbles which equal or exceed 4 inches in diameter. Of this 10 per cent, 6 per cent consists of reddish granite, and 4 per cent of the dark-colored diorites and diabases, indicating that very few rocks originating as lavas or dike rocks are present, since they are not sufficient in number to equal even one per cent of the total.
The source of the granitic rocks occurring as pebbles in the gravel ridges is in Canada. If a line be drawn from the extreme northeastern corner of Lake Ontario westward to the most eastern angle of Georgian bay, and thence along the northern shore of this bay and of the channel north of Manitoulin island westward as far as Marquette, on the southern shore of Lake Superior, then a long east and west line would be secured, south of which the prevailing rocks are limestone, with lesser amounts of sandstone and shale, while north of this line the deep-seated granitic rocks are common, forming the prevailing rock ledges over large extents of country. It is the restriction of the granitic rocks to these Canadian territories, among areas not too remote from Ohio, which gives greatest assurance to the average observer of the northern origin of the pebbles found in the gravel ridges south of Dayton.
It requires some familiarity with fossils and with the different subdivisions of the rocks in which they occur to be able to appreciate that a certain pebble indicates derivation from a northern source, and hence a southward flow of waters. However, very little information is needed to recognize certain pebbles as granite, and as different from any rock found in the form of ledges within Ohio or Indiana. Hence, the presence of granite pebbles is more commonly cited as an evidence of the northern source of the pebbles in the gravel ridges, although the fossils of some of the limestone pebbles furnish equally definite evidence.
25. The Quartzite, Gneiss, and Other Metamorphic Rocks of Ontario
Sandstone, under the influence of great pressure and heat, in the presence of moisture, is altered into a much harder rock called quartzite. This frequently has a whitish or reddish color, and often has a crystalline, more [p.72] or less glassy appearance, owing to the enlargement of the quartz particles of the original sandstone
Under the same influences of abnormal pressure and heat, granitic rocks have been altered to rocks in which the minerals are more or less arranged in bands or thin layers, often differing in color, and sometimes more or less contorted. These granitic rocks are then called gneisses.
[Photo: The Lambert boulder, 46 feet in circumference, found in the woods twelve miles west of Dayton. One of the granitic rocks of Canadian origin.] [p.73]
When altered sandstones, argillaceous rocks, or granites are so abundantly supplied with mica or hornblende, arranged in approximately parallel directions, that the rock splits more or less readily parallel to these minerals, the rock is called a mica or hornblende schist.
Quartzites, gneisses, and schists are abundantly represented among the pebbles of the gravel ridges south of Dayton. They form about 6 per cent of the total number of the larger sized pebbles.
Since they occur, as solid ledges in this section of the country, only north of the boundary line separating the limestone areas from the igneous rock areas, in other words, north of Lake Ontario, Georgian bay, the north channel of Lake Huron, and Lake Superior, it is evident that the presence of quartzites, gneisses and schists among the pebbles is further evidence, if any were needed, of the northern origin of these pebbles.
26. The Streams Producing the Gravel Ridges Were of Short Length
Although the evidence is clear that the streams which deposited the gravel ridges south of Dayton obtained these materials from the north, this does not prove that these streams were of any great length. In other words, running water may have been only one of the transportation agencies bringing these rocks from their northern sources. It may have been only the last active agency, and the one which produced the least result, as far as the distance they actually moved the rocks is concerned. Previously to the action of the water, some other transportation agency may have been at work.
This transportation agency was the ice, in the form of a glacier of enormous size.
We shall see later that the streams producing the gravel ridges probably were of short length, in some cases only a few miles. However, no matter how short, if their direction of flow had been northward, some of the pebbles would show evidence of southern origin, and this is not the case. [p.74]
[Photo: Glacial striae running 15 degrees east of south across the upper surface of the Brassfield limestone. Photograph taken along the road crossing the hill a little over a mile west of Simms station, two and a half miles northeast of Harshmanville.]
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