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Rh one of them. For example, in Ohio (Northwestern Ohio) it is very close and clayey, the upper part being free from bowlders and stones. In Minnesota (Central Minnesota), the stones and bowlders are more generally disseminated throughout the whole, and it shows much more sand. Hence, in the latter State it will allow the slow passage of water through it—a fact exceedingly fortunate for the agricultural capacity of the soils that are based on it.

Perhaps there should be added to this description of the drifts another member, which may be denominated No. 4.

No. 4.—This, however, is so inconstant and so often runs into the last, that it is hardly worthy of special designation. When present, it lies below No. 3, and immediately over the rock. It consists of gravel and bowlders, more or less mingled with clay. It is the great water-reservoir that supplies deep wells, and through it there is a constant slow drainage into deep valleys and excavations. It gives rise to springs at the base of the river-bluffs, and to artesian wells, when the confining stratum of hard-pan above is penetrated in regions of favorable slope. In Northwestern Ohio is a most wonderful series of artesian wells that depend entirely upon this fortunate combination of circumstances. This member of the drift sometimes consists largely of assorted materials, as sand and gravel. This is indicated by the issuing of considerable quantities of such sand from artesian wells that penetrate it, when the force of the current of water is sufficient to bring it to the surface. Instances have occurred of the collapse of the overlying clay and hard-pan, on the removal in this way of large quantities of sand. Along the upper side of this member, the materials are apt to be firmly cemented by iron and carbonate of lime, into a very firm, even rocky crust. Such cemented gravel and sand is seldom over two feet thick, yet well-borers, on reaching it, often mistake it for the bed-rock. They pass through it, and usually find a copious flow of excellent water. The announcement is then promulgated that that well was drilled through the rock. Hence it is a popular error that, in order to obtain water of the purest quality, it is necessary to sink a well "through the rock." This member, though, is not always found in penetrating the drift to the rock. It may be here stated, also, that, when No. 4 is present, the bed-rock does not show so plainly the marks of glaciation; but, when No. 3 extends to the rock, the surface of the bed-rock is almost invariably marked with the well-known glacier-etchings.

Having taken this survey of the component parts of the drift, it will be well to bring them into a general view, as illustrated by the preceding diagram (Fig. 3), in which the figures represent the same members as in the previous illustrations. It shows a general section of the drift, from Toledo to Shelby County, Ohio, and is based on extended observations, the results of which are to appear in the forthcoming reports of the "Geological Survey of Ohio." The six ridges