THE PLEISTOCENE OR GLACIAL PERIOD. 



347 



Fig. 482. — Stria? on bed-rock, Kingston, Des Moines Count}', la. (la. Geol. Surv. 



Fig. 483. — Grooves in limestone on Kelley's Island, Lake Erie. The grooves show 

 by their lack of strict parallelism that different parts of the grooving were accom- 

 plished at somewhat different times. The foot-rule indicates the scale, and its 

 shadow defines the groove. (U. S. Geol. Surv.) 



