GLACIAL EPOCH. 



547 



covered with a more regularly stratified material, consisting of sand and 

 gravel, apparently subsequently deposited from water. This is particu- 

 larly the case in the basin of 

 the Mississippi, as e. g., in 

 Ohio, Illinois, and Iowa. It is 

 probable, however, that this be- 

 longs to the next epoch, Cham- 

 plain. Sometimes irregular 



Wi 





m 



o oO °o ° 



m 





3 - ' o ° 



& 



mound -like deposits are left in FlG . 924.— Section on Rush Creek, near Mono Lake, 



the retreat of the ice. These California. 



are called Jcames, drumlins, etc. The conditions under which these are 



formed are imperfectly understood. 



Fig. 925,— Section of Orange Sand, Mississippi (after HiJgard). 



We have said that the deposit is peculiar. Nothing resembling it 

 is found anywhere in tropical or low-latitude countries. In the South- 



Fig. 926.— Section of Orange Sand, Mississippi (after Hilgard). 



ern Atlantic States, for instance, the soil is mostly either the insoluble 

 residue of rocks decomposed in situ, or else consists of neatly- stratified 

 sands and clays. 



Drift-material is not usually represented on geological maps, since 

 it covers all kinds of country rock ; or else the colors representing the 



Fig. 927.— Outcropping— Eroded Country Rock overlaid by Drift. 



