272 



MATERIALS AND THEIR ARRANGEMENT 



limestones and fine-grained sandstones. During the exposure of the 

 sediments, a shower may pass, and raindrop impressions (Fig. 245) 

 be made which are subsequently filled by fine sediment and preserved. 

 Unconformities. Figs. 246, 247, and 248, show, in each case, one 

 set of beds out of harmony with another set. This relation is one of 



Fig. 245. Raindrop impressions. (Brigham.) 



Fig. 246. Unconformity between the Devonian (the thick-bedded rock) below, 

 and the Coal Measures (thin-bedded and broken) above. Iowa. (Udden.) 



