METHODS OF PALAEONTOLOGICAL INQUIRY. 65 



which have been left standing assume the most bizarre outlines, 

 often strikingly imitating architectural forms, towers, palaces, 

 pinnacles, and spires of some ruined city of the giants. The 

 weird, fantastic shapes more resemble the " baseless fabric of 

 a vision " than the topographical forms of everyday reality. 



The principal agent in this enormous work of destruction is 

 the rain, which dissolves out the calcareous cement (CaC03) 

 that binds together the insoluble particles of sand or clay into 

 a firm rock. True, the total amount of atmospheric precipitation 

 is small, but the rainfall is heavy when it does come, and often 

 the dry water courses are in an incredibly short time converted 

 into rushing torrents. Experience soon teaches the explorer 

 not to put his camp on low ground, but always to select a point 

 to which the flood waters never rise. When the rain can reach 

 freshly exposed surfaces of rock, the disintegration is often 

 excessively rapid. I have observed a firm rock to be thoroughly 

 disintegrated to the depth of -^^ of an inch by a single light 

 shower, lasting only a few moments. In the Bridger Bad 

 Lands the Princeton expedition of 1885, in excavating the skele- 

 ton of a large Uintat/icriiuii, dug out a great hole, the rock from 

 which was piled into a cairn. When we revisited the same 

 spot a year later, the cairn was found to be weathered down 

 into a low hummock of soil, and the hole was so filled up as to 

 be hardly recognizable. From these observations one might 

 infer that the progress of rock decay must be exceedingly 

 rapid, but as a matter of fact, it is very slow. The rainfall is 

 limited, and of even more importance is the fact that the soil 

 produced by the disintegration of the rocks, which covers all 

 the buttes save the vertical faces, becomes, when wet, almost 

 impervious to water. A heavy downpour of several hours' 

 duration will wet this soil to the depth of only two or three 

 inches. It is this waterproof soil which throws off the rain, 

 causing it to gather in the gulleys and water courses, and to 

 form those sudden and violent floods which to be appreciated 

 must be seen. 



The exact forms assumed by the bad land "buttes" (or emi- 

 nences), as in the case of other topographical forms, depend 

 upon the interaction of several factors, such as the manner in 



