CHAPTER V I I
PERIODS OF ADVANCE AND RECESSION OF THE GLACIAL ICE FRONT
[Photo: Second hollow west of southern end of Cornfield hollow, in the kame area west of the Lohman ridge, south of Calvary cemetery. In this case the depth of the hollow is indicated by the curvature of the fence.]
49. More Than One Advance of the Glacial Ice Sheet
Even the Alpine glaciers vary in length. They move farther down the valley in winter and melt back in summer. A succession of warm summers, with comparatively little snow fall, may cause the ice front to melt back farther. Lter, it may advance again. Considerable advances have been noted recently in case of some of the Alaskan glaciers, caused apparently by the shaking down of unusual quantities of snow from the upper mountain slopes, as the result of several earthquake shocks. The advance of the ice front lagged several years behind that of the great snow slides which accompanied the earthquake. Variations in the position of the ice front due to climatic changes, however, are likely to prove of longer duration. [p. 111]
During the melting back of the ice front, the various deposits at its margin form the terminal moraine, beyond which extends the outwash plain formed by the numerous streams escaping from the ice. Later, when the ice front readvanced, the debris-laden base of the ice sheet might be pushed on top of the earlier sand and gravel deposits, so as to leave a layer of till on evidently stream deposited materials.
In describing the glacial deposits exposed at the quarries at Beavertown, Leverett states that the main mass of till, 5 to 10 feet thick, overlies poorly assorted gravel and sand, horizontally bedded, while the latter often rests on a thin layer of till, in contact with the rock. Here the lower till evidently represents a remnant of an earlier ground moraine, covered with gravels and sand by streams issuing from the retreating glacier. The upper till represents a later ground moraine, which toward the margin of the readvancing glacier rode over the sands and gravels deposited during its period of retreat.
Till resting on considerable thicknesses of gravel may be seen also in the southeastern part of Dayton, along the northern edge of the hill land forming Ohmer Park. It is exposed at the numerous gravel pits at present to be seen south of the baseball park in east Dayton. Here the till frequently is 1 to 4 feet thick. It evidently rises from the low lands, on the north, toward the south, and indicates that the ice front was pushed up and over the water-laid deposits of sand and gravel, sufficiently to leave upon them the till, embedded within its lower parts.
Some of these changes in the ice front probably were of very minor character. At the great gravel pit northeast of the Calvary cemetery, a thin layer of till, only about 2 feet thick, projects southward into the gravels, being both underlaid and overlaid by gravel and sand. Similar thin layers of till occur in the gravel pit north of the reservoir along the Stroop road, on the Moraine farm.
When these deposits of till and gravel are of very local character it easily is possible that the same part of the ice front could furnish gravel and sand from the subglacial streams and till from the melting base of the ice sheet. [p. 112]
Some of the recessions and advances of the ice sheet involved the shifting of the ice front for such long distances, and involved such long periods of time, that it has been found convenient to give them names. The periods of advance of the ice sheet are known as those of invasion. Those of the melting back of the ice front have been called the interglacial intervals, because during the latter the ice disappeared over a large part of the marginal portions of the ice-covered territory. During the interglacial intervals both plants and animals pervaded the ice-freed country. The top layers of the glacial deposits were converted gradually into soil. The surface rocks began to show the influences of exposure to the weather. Their color changed to brownish and the included minerals began to decay.
Plant and animal life invaded the country. In the swampy areas, peat was formed. In the ponds, the accumulations of millions of shells, often very minute, gave rise to marl. In these various ways the interglacial intervals left records of their former existence.
The collecting of the evidence of the more prominent advances and retreats of the ice front of the former great continental glacial ice sheet represents the monumental work of quite a number of the most able American geologists, among whom may be mentioned Chamberlin, Salisbury, Leverett, Calvin, Upham, and Taylor.
The following list includes the names of the chief periods of invasion and retreat of the ice front, the invasions resulting in the deposition of drift and the retreats being accompanied by the formation of soil. In this list the first deposit of drift is placed at the bottom of the list and the last deposit at the top.
10. The present period of complete disappearance of the continental ice sheet.
9. The Wisconsin drift, the fifth invasion.
8. The Peorian soil, the fourth interglacial interval.
7. The Iowan drift, the fourth invasion.
6. The Sangamon soil, the third interglacial interval.
5. The Illinoian drift, the third invasion. [p. 113]
[Map: Map showing different positions of the ice front during the retreat of the Wisconsin ice
sheet. Redrawn from Leverett’s Monograph on the “Glacial Formations and Drainage Features
of the Erie and Ohio Basins.”] [p. 114]
4. The Yarmouth soil, the second interglacial interval.
3. The Kansan drift, the second invasion.
2. The Aftonian soil, the first known interglacial interval.
1. The Pre-Kansan drift, the earliest known invasion.
The names for these deposits and periods are chosen from those areas in which the drifts and soils are typically exposed. The names Wisconsin, Iowan, Illinoian, Kansan, and Pre-Kansan are self-explanatory. The town Peoria and the river Sangamon are in Illinois. Yarmouth and Afton are towns in Iowa.
51. The Earlier Glacial Invasions of Ohio
No traces of the Pre-Kansan or Kansan invasions have been identified in southwestern Ohio. Both are chiefly of western distribution, although certain deposits in the northwestern part of Pennsylvania are regarded by Leverett as contemporaneous with the Kansan deposits.
The third, or Illinoian invasion not only reached the Ohio river, but crossed over into the limits of Kentucky in the area south of Cincinnat. In wester Ohio, the terminal moraine marking its southern boundary, passed from Chillicothe southwestward to Ripley, on the Ohio river, and then along the river almost as far westward as Cincinnati. Before reaching that city, however, it entered Kentucky and took a southwesterly course as far as the bend of the Ohio river east of Warsaw. Westward, it followed the southern side of the Ohio river to the vicinity of Marble Hill, a small village south of Madison, in Indiana, beyond which the boundary entered the state of Indiana.
The Iowan invasion also appears to have been chiefly of western distribution, and its identification within the limits of Ohio may be said to remain uncertain.
52. The Terminal Moraine of the Earlier Part of the Wisconsin Invasion, in Ohio
The earlier part of the Wisconsin invasion of the continental ice sheet took place in the form of a series of broad lobes, 60 to 80 miles wide, occupying the larger drainage basins. Of these, the Miami lobe, at its period [p. 115] of greatest advance, formed an ice front reaching from Xenia to Waynesville, Lebanon and Mason. It extended almost as far south as Hartwell, 5 or 6 miles north of Cincinnati. North of Hartwell the front of this lobe turned northwestward, toward Hamilton; then southwest for a short distance, and again northwest, as far as Brookville, in Indiana, finally turning northward toward Connersville. This is the Hartwell moraine.
53. The Germantown, Eaton, and Englewood Divisions of the Dayton Moraine
The most southern division of the Dayton moraine extended beyond Germantown. This may be traced from east of Harshmanville, across Huffman hill, to the bluffs, south of Dayton, and thence east of the Miami valley, by way of Carrmonte, the Moraine farm, and Delco Dell, to the hills east of Miamisburg and Franklin. From Franklin this moraine may be traced westward, south of Germantown, to Camden, and thence to Richmond, in Indiana.
It is to this most southern extension of the late Wisconsin ice sheet, giving rise to the Germantown moraine, that the gravel ridges south of Dayton owe their origin. This Germantown division of the Dayton moraine usually rises about 20 or 30 feet above the level of the land on its southern side, although locally this elevation may rise to 50 feet. Roads entering this morainal territory from the south often rise abruptly on reaching the moraine. The width of the moraine, from north to south, is about two miles.
The middle or Eaton division of the Dayton moraine extends from Dayton View southwestward to a point three miles north of Germantown, and then curves northwestward to Farmersville, Ingomar, West Alexandria, and Eaton, passing east of New Paris, and west of New Madison. This middle or Eaton division of the Dayton moraine may be recognized readily by the very large number of boulders found on its surface. In a field near West Alexandria, Professor Orton actually counted more than 1,200 boulders, exceeding 2 feet in diameter, per acre. The majority of [p. 116] the larger boulders have a volume of 10 to 20 cubic feet, but some attain a volume of 100 cubic feet, or more. Most of these boulders consist of Canadian granites, green-stones, schists, and quartzites. But very few limestones or boulders of local origin, in Ohio, are present. The vast majority are subangular, or only partially rounded. Scarcely one in a hundred shows glacial scratching. Evidently, many of these boulders were carried along chiefly within the body of the ice, rather than shoved along at its bottom. North of Dayton, this boulder belt may be traced from Dayton View to the northern part of Riverdale, thence along the eastern side of the Miami, to West Charlestown, Christiansburg, and St. Paris. Its usual width, where it can be distinguished from the two other divisions of the Dayton moraine, is two miles or somewhat less. The southern border of this Eaton division of the moraine usually has a more gradual rise above the lands immediately southward than is true of the southern border of the Camden division of the moraine.
The northern or Englewood division of the Dayton moraine extends from the area east of Troy southwestward, crossing the Stillwater valley at Englewood, thence passing to Pyrmont, Sonora, Ithaca and Fort Jefferson. This division of the moraine also is covered with an abundance of boulders, but not in such great numbers or of such large size as in the case of the middle or Eaton division. The width of this division of the moraine, measuring across the moraine from north to south, varies from two to three miles.
These three divisions of the Dayton moraine represent three distinct stages in the retreat of the Wisconsin glacier. Each division records a period during which the glacial ice front remained comparatively stationary, shifting forward and backward within comparatively narrow limits. The spaces between consecutive divisions record periods during which the melting back of the ice front was too rapid to admit of the deposition of thick layers of till and other glacial deposits.
Northeast of Dayton the three divisions of the Dayton moraine approach each other sufficiently to more or less overlap. Hence, within this area, as far as Bellefontaine, it sometimes is impossible to distinguish the [p. 117]
[Photo: View of the broad shallow valley between the Walden ridge (on the right) and the Schumacker ridge (seen only in the immediate foreground and thence toward the left.) The valley extends across this view from right to left. The abandoned barn on the Walden ridge is just beyond the right margin of this view.] [p. 118]
component divisions from each other with sufficient accuracy to establish more than their general trend.
There were many such periods of comparative rest and of more rapid retreat during the decline of the Wisconsin glacier. At each period of rest a new terminal moraine was formed, ten, twenty, thirty, or some other number of miles back from the moraine formed at the preceding halt of the retreat. One of these later formed moraines extended almost as far south as Greenville. Another almost reached Versailles. Another reached the northern border of the Loramie reservoir. Another reached Celina and St. Marys. Another stopped north of Lima. Another reached a point north of Findlay. Still others terminated at points farther northward, but included within the boundaries of Canada.
54. Buried Soils
Each period of retreat of the glacial ice sheet exposed more and more of the ground to the activities of the sun. Under the influence of heat and cold, moisture and dryness, the ground began to weather. Owing to the presence of very small quantities of iron, it gradually assumed a brownish color. Seeds were blown in from southern territories, or were carried in by animals. The ground, barren at first, became clothed with vegetation. The roots, penetrating the soil, loosened the ground, and, by their decay, enriched it. Burrowing insects and worms brought up the finer particles of soil to the top and left the coarser particles behind. The final product was a surface layer of loosened earth, more or less intermingled with decayed vegetable material, which might be recognized by any one as soil.
Even when a soil formed during some interglacial period was buried under the deposits of some later readvance of the ice sheet, this buried material can be recognized as soil. In some cases it can be recognized as soil by the presence of the tortuous but very narrow cavities left by the roots. In other cases, the presence of burrowing insects assists in identifying it. Roots and parts of trunks of trees may be left in their original position. The brown color may be preserved. Of course, where the quantity of included vegetable material was so great as to color the soil black, the latter can be identified most readily. [p. 119]
[Photo: View at the head of the gully located east of the Emrick farm, looking from the high land along the line between VanBuren and Washington townships southwestward. The gully starts at the cluster of trees on the right. A man stands on the ridge in the middle distance. Farther back is seen the northward extension of the Walden ridge.] [p. 120]
Such buried soils occur at numerous localities in Ohio.
One of these ancient soils is exposed on the eastern bank of Twin creek, about a mile east of Germantown, immediately south of the locality where the traction road begins to descend the hill land rapidly, going westward. Here thick deposits of till line the western side of the creek, forming steep slopes. Only one or two feet above the level of the creek, darkened, almost black soil is exposed when the stream washes away the material which has slumped down from higher levels on the bank. In this soil Professor Orton recognized fragments of coniferous wood (probably cedar), cedar berries, grasses, sedges, and sphagnous mosses. To Professor G. F. Wright the deposit suggested a peat layer formed at the bottom of a kettle hole, a depression in part of a kettle moraine. Possibly this soil represents the interval between the deposition of the earlier and later Wisconsin advances of the glacial ice sheet.
At Wilmington, Ohio, Doctor Austin discovered in a similar peat layer the remains of beetles and other animal life indicating a general return to living conditions during the interval occupied by this period of peat formation. In fact, the border of life probably never was far south form the immediate front of the ice sheet. In the Alps, plants spring up almost in contact with the ice, as soon as the ground is exposed to the warming influences of the sun. Some of the heavy seeded trees, like those bearing the heavy nuts, such as hickory and walnuts, and including also the oaks, may have taken longer periods of time to return to their original habitats, while trees with seeds that are carried by the wind, such as maples and poplars, certainly returned much faster.[p. 121] [p. 122]
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