CHAPTER V
THE WORK OF GLACIERS
The drift. The surface of northeastern North America, as far south as the Ohio and Missouri rivers, is generally covered by the drift,—a formation which is quite unlike any which we have so far studied. A section of it, such as that illustrated in [Figure 87], shows that for the most part it is unstratified, consisting of clay, sand, pebbles, and even large bowlders, all mingled pell- mell together. The agent which laid the drift is one which can carry a load of material of all sizes, from the largest bowlder to the finest clay, and deposit it without sorting.
Fig. 88. Characteristic Pebbles from the Drift
No. 1 has six facets; No. 4, originally a rounded river pebble, has been nibbled down to one flat face; Nos. 3 and 5 are battered subangular fragments on one side only
The stones of the drift are of many kinds. The region from which it was gathered may well have been large in order to supply these many different varieties of rocks. Pebbles and bowlders have been left far from their original homes, as may be seen in southern Iowa, where the drift contains nuggets of copper brought from the region about Lake Superior. The agent which laid the drift is one able to gather its load over a large area and carry it a long way.
