Man and the Glacial Period

by G. Frederick Wright

In the central part of New York the remarkable series of “Finger Lakes,” tributary to Lake Ontario and emptying into it through the Oswego and Genesee Rivers, all have a glacial origin. Probably, however, they are not due in any great degree to glacial erosion, but they seem to occupy north-and-south valleys which had been largely formed by streams running towards the St. Lawrence when there was, by some means (probably through the Mohawk River), a much deeper outlet than now exists, but which has been filled up and obliterated by glacial débris. The ice-movement naturally centred itself more or less in these north-and-south valleys, and hence somewhat enlarged them, but probably did not deepen them. The ice, however, did prevent them from becoming filled with sediment, and on its final retreat gave place to water.

Between these lakes and Lake Ontario, also, and extending east and west nearly all the way from Syracuse to Rochester, there is a remarkable series of hills, from one hundred to two or three hundred feet in height, composed of glacial débris. But while the range extends east and west, the axis of the individual hills lies nearly north and south. These are probably remnants of a morainic accumulation which were made during a pause in the first advance of the ice, and were finally sculptured into their present shape by the onward movement of the ice. These are really “drumlins,” similar to those already described in northeastern Massachusetts and southeastern New Hampshire. In the valley of central New York these have determined the lines of drainage of the “Finger Lakes,” and formed dams across the natural outlets of nearly all of them.

North of the State of New York the innumerable lakes in Canada are all of glacial origin, being mostly due to depressions of the nature of kettle-holes, or to the damming up of old outlets by glacial deposits. A pretty well-marked line of moraine hills, formed probably as terminal deposits in the later stages of the Ice age, runs from near the eastern end of Lake Ontario to the Georgian Bay, passing south of Lake Simcoe.

The Mississippi Basin.

The physical geography of the glaciated region north of the Ohio River is so much simpler than that of New England and the Middle States, that its characteristics can be briefly stated. Ohio, Indiana, and Illinois are covered with nearly parallel strata of rock mostly of the Carboniferous age. In general, the surface slopes gently to the west; the average elevation of Ohio being about a thousand feet above tide, while that of the Great Lakes to the north and of the middle portion of the Mississippi Valley is less than six hundred feet. The glacial deposits are spread in a pretty even sheet over the area which was reached by the ice in these States, and the lines of moraine, of which a dozen or more have been partially traced in receding order, are much less clearly marked than they are in New England, or in Michigan, and the States farther to the northwest.

The line marking the southern limit attained by the ice of the Glacial period in these three States is as follows: Entering Ohio in Columbiana County, about ten miles north of the Ohio River, the glacial boundary runs westward through New Lisbon to Canton in Stark County, and thence to Millersburg in Holmes County. A few miles west of this place it turns abruptly south, passing through Danville in Knox County, Newark in Licking County, Lancaster in Fairfield County, to Adelphi in Ross County. Thence bearing more westward it passes through Chillicothe to southeastern Highland County and northwestern Adams, reaching the Ohio River near Ripley, in Clermont County. Thence, following the north bank of the Ohio River to Cincinnati, it crosses the river, and after extending through the northern part of Boone County, Kentucky, and recrossing the river to Indiana, not far from Rising Sun, it again follows approximately the north bank of the river to within about ten miles of Louisville, Ky., where it bends northward running through Clarke, Scott, Jackson, Bartholomew, and Brown Counties to Martinsville, in Morgan County, where it turns again west and south and follows approximately the West Branch of the White River through Owen, Greene, and Knox Counties, where it crosses the main stream of White River, and, continuing through Gibson and Posey Counties, crosses the Wabash River near New Harmony.

In Illinois the line still continues southwesterly through White, Gallatin, Saline, and Williamson Counties, where it reaches its southern limit near Carbondale, in latitude 37° 40’, and from this point trends northwestward, approximately following the northeastern bluff of the Mississippi River, to the vicinity of Carondelet, Mo., a short distance south of St. Louis.

Beyond the Mississippi the line follows approximately the course of the Missouri River across Missouri, and continues westward to the vicinity of Manhattan, in Kansas, where it turns northward, keeping about a hundred miles west of the Missouri River, through eastern Kansas and Nebraska, and striking the river near the mouth of the Niobrara, in South Dakota. From there the line follows approximately the course of the Missouri River to the vicinity of Fort Benton, in northwestern Montana, where the line again bears more northward, running into British America.

It is still in dispute whether the ice extended from the eastern centre far enough west to join the ice-movement from the Rocky Mountain plateau. Dr. George M. Dawson[BC] is of the opinion that it did not, but that there was a belt of a hundred miles or more, east of the Rocky Mountains, which was never covered by true glacial ice. Mr. Upham[BD] is equally confident that the two ice-movements became confluent, and united upon the western plateau of Manitoba. The opportunity for such a difference of opinion arises in the difficulty sometimes encountered of distinguishing between a direct glacial deposit and a deposit taking place in water containing boulder-laden icebergs. Where Mr. Upham supposes the ice-fields of the east and of the west to have been confluent in western Manitoba, Dr. Dawson supposes there was an extensive subsidence of the land sufficient to admit the waters of the ocean. Leaving this question for the present undetermined, we will now rapidly summarise the glacial phenomena west of the third meridian from Washington (which corresponds nearly with the western boundary of Pennsylvania), and east of the Rocky Mountains.

[BC] Transactions of the Royal Society of Canada, vol. viii, sec. iv, pp. 54-74.