OBJECTIONS TO LACUSTRINE THEORY 711 



stratification presented b}^ the fine deposits, the prevalency of remains of 

 large land animals and an entire absence of fish and aquatic invertebrate 

 fossils, the complete merging of the terranes on the one hand into un- 

 doubted eolic deposits and on the other hand into unquestionable river 

 formations, and the existence of climatic conditions precluding the devel- 

 opment of extensive bodies of quiet waters. 



Weakness of the Fluviatile Hypothesis 



The origin of the Great Plains deposits through means of the ag- 

 grading action of rivers is urged mainly because of (1) the well known 

 building up process of certain streams in a sinking area; (2) the vast 

 and even surface of many fluviatile plains; (3) the presence of a great 

 mountain background capable of supplying enormous quantities of rock- 

 waste; (4) the capacity of rivers to form extensive deposits of fine text- 

 ure and even stratification; (5) the importance of coarse piedmont de- 

 posits in dry mountainous regions; (6) the frequent evidences of 

 subaerial exposure throughout the terranes, and (7) the resemblances of 

 river deposits to those of the great intermont basins of arid lands. These 

 several features may be briefiy considered. In so far as the Great Plains 

 are concerned, I am inclined to agree with Davis that the consideration 

 ol the fluviatile aspects of their origin has been not so much directed 

 toward the actual observation of facts in the Eocky Mountain region as 

 toward the theoretical discussion of recorded observations. Neverthe- 

 less, this discussion is of the highest benefit. 



Since after debouching from the desert ranges torrential streams soon 

 wither away, it is generally assumed that their loads of rock-waste are at 

 once dropped, and that piedmont plains are rapidly built up. The idea 

 is well expressed by Huntington^^ when he speaks of southern Arizona 

 "mountain ranges half smothered in interminable slopes of gravel which 

 head far up on the flank of the hills and sometimes cover the passes." 

 The extension of this local conception to a broad generalization embrac- 

 ing, for example, so vast an area as the plains east of the Eocky Moun- 

 tains, seems but a step. Deductively great importance is attached to the 

 aggrading action of streams. 



In the Great Basin region, where excessive dryness prevails, the inter- 

 mont plains appear not to be so deeply covered by mountain waste as was 

 once supposed. There are now known many cases in which beneath a 

 veneer of soil and rock debris such plains have well defined rock-floors.®^ 



w Harper's Magazine, vol. cxxlli, 1911, p. 54. 

 " Bull. Geol. Soc. America, vol. 19, 1908, p. 



