2 ON THE FRESH-WATER GLACIAL DRIFT 



because it expresses what I conceive to be the mode of its origin. Its epoch nearly 

 approaches that of the alluvium. It is so recent that in many cases the buried 

 timber is not decayed or even discolored. As it is due to glacier action from the 

 north, a force which was universal, it must have its counterpart in Northern Europe 

 and Asia. 



After these general observations I proceed with the descriptions in detail. The 

 three members are as follows, reckoning in the order of superposition from the 

 surface downwards: — 



1st. Coarse sand, gravel, loam, and hard pan, with large boulders of northern 

 rocks, occupying the surface and the heights of land, with little stratification. 



2d. Sand and gravel less coarse than No. 1, with irregular bands of clay some- 

 what laminated, and boulders smaller than in No. 1. 



3d. Fine laminated sandy and marly clay of great thicloiess, of a red, purple, 

 blue, and ash color, with few boulders and little gravel, occupying the valleys of 

 the lakes and rivers. 



Wherever there is a great thickness of the superficial materials these divisions 

 can be readily traced, and always in' the same order, as shown in the accompanying 

 section. The laminated clays are invariably at the bottom where more than one 

 member exists, and generally rest on the indurated rocks. 



Number one occupies the height of land, and frequently lies upon the rock for- 

 mations Avithout intervention of the other drift beds. It is always coarse and more 

 or less confused. What is known among well-diggers, and canal and railroad 

 contractors, as "hard pan," belongs to this member. The hard pan is the result 

 of a mixture of clay, sand, and gravel, or fragments of rocks, in a confused or imper- 

 fectly stratified condition, rendered compact by the nature of the materials and 

 by pressure. 



There is a modified form of the drift in and along the edges of the valleys of 

 streams, heretofore known as "valley drift," which, with the resulting terraces, is 

 due to changes and causes, to which reference will be hereafter made. Member 

 number one is the seat of the Moraine hillocks and depressions that mark the sum- 

 mits of the country. It is always coarse and imperfectly stratified. The gravel is 

 not derived whoEy from distant and northern rocks. The strata, which underlie 

 the drift at different points, are also represented. Where these strata are soft the 

 fragments, torn off by the ice movement, are more easily pulverized, and are, there- 

 fore, not transported as far as those of the hard, and especially of the tough igneous 

 rocks. 



Sandstone, limestone, and shale from the coal series, and from the Devonian beds, 

 are common. These are in general not as completely rounded, but are more elon- 

 gated and flatter, with their edges less worn. But representatives from all the 

 rocky strata to the north can be found including the Potsdam sandstone, and other 

 lower Silurian beds; also trap, trachyte, granite, sienite, gneiss, and conglome- 

 rate, with the contents of dykes and mineral veins, pieces of iron ore, and boulders 

 of native copper, from Lake Superior. 



This upper member of the drift is distinguished by evidences of violence in the 

 action of the glacial forces. It contains the largest and most numerous boulders. 



