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5. Comparison of models.—Turning from Fig. 1, which shows the deposits as they exist to-day, to Fig. 2, which shows the theoretical conditions of formation, it will be seen that the northern half is covered with ice, from which is issuing an esker river. The ice in the second is represented as fitting into the intercuspate hollows shown at the head of the sand-plain in the first model, and is from one hundred to three hundred and fifty feet thick. Toward the rock hills on the east and west it falls off, as would be the case where the ground was higher. The ice has a convex curving surface in front, with contours softened by melting, while on top it is approximately level with here and there surface streams, moulins, and perhaps a little lake.

The three little knobs of older date than the sand-plain standing near its front margin, can be seen in both models. The till-covered hills of bed rock are also the same in the two, but in the second the water stands higher up on their sides. The second model being a trifle larger, a little more of them is shown on the edges. The group of hummocky kames, shown to the southwest of the sand-plain in the first model, is covered in the second by the body of standing water into which the esker river flowed.

6. Esker river.—Professor Chamberlin has given us the very helpful distinction between "kame" and "esker" (osar), from the use of the words in Scotland and Ireland respectively. The former is used by the Scotch for their irregular mounds and hillocks, so typically shown in that country, and which, if developed at all in lines, have their axes at right angles to the direction of ice flow; and the latter for the Irish ridges of sand and gravel, beds of former glacial rivers, which have their axes parallel to the lines of motion in the ice. This terminology is here followed.

In the first model the esker, a ridge of sand and gravel, fairly stratified, may be traced from the middle of the northern end, where it is some ten to twenty feet high, curving eastward and then southward again, gently rising to some seventy feet above the alluvial plain shown on the northwest corner of the model of the sand-plain, and one hundred and thirty feet above mean tide.