Handbook of Paleontology 25 



deposits are most prominently illustrated by dunes and 

 loess. The sand grains composing dunes are mostly 

 quartz and are well rounded. Rocks formed from such 

 deposits are characterized by the rounded character of 

 the quartz grains and lack of fossils. Loess is a pale to 

 buff-yellow or brown deposit composed of quartz, feld- 

 spar, clay, calcite, mica etc. The particles are finer than 

 those in ordinary sands, sharply angular and there is an 

 absence of stratification characteristic of water-laid ma- 

 terial. Such deposits have few fossils and those that are 

 found are land forms such as snails or bones of animals. 

 Concretions of carbonate of lime and oxide of iron are 

 characteristic features of these deposits and often assume 

 odd shapes. 



Among deposits due to the agency of water are desert 

 deposits in arid interior drainage basins. The land waste 

 of the slopes of the basins is constantly moving toward 

 the interior either into permanent lakes which they slowly 

 fill up or into temporary lakes or playas. Rainwash, 

 streams and wind drift play a part in the formation of 

 these deposits. Layers of salt and gypsum often charac- 

 terize such deposits and they are apt to show red colora- 

 tion, less often yellow. This coloring is due to oxidization 

 of the iron compounds in the rock and the lack of vege- 

 tation which through its decay would reduce or deoxidize 

 the iron compounds and decolorize them. In humid re- 

 gions, that is, where the rainfall is considerable, basinlike 

 depressions of the continents become lake basin areas 

 which receive deposits from streams. The shallow, more 

 swampy areas show mud and clay deposits intermingled 

 with organic matter from decaying vegetation. Rivers 

 draining high mountain ranges are overloaded with mate- 

 rial which they drop when they reach the foot of the 



