348 



GEOLOGY 



at all elevations where the drift occurs. The markings on the bed- 

 rock beneath the drift are so like those on the stones of the drift, that 

 community of origin cannot be doubted. 



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Fig. 484. — The radiation of stria? in the Green Bay glacial lobe, and in the west part 

 of the Lake Michigan lobe, during the last glacial epoch. 



The striae on the bed-rock beneath the drift are generally approxi- 

 mately parallel in any given locality, and tolerably constant in direc- 

 tion over considerable areas. When large areas are studied, the striae 

 are sometimes found to be far from parallel. In general, their depar- 



