6 4 



BIOLOGICAL LECTURES. 



Into this great body of water the streams incessantly brought 

 quantities of gravel, sand, clay, and mud, which were sorted 

 out by the still waters of the lake and deposited in layers, 

 which, however, are often irregular, changing from point to 

 point in a very puzzling way. The strata are, for the most 

 part, only imperfectly indurated and quite soft, so that they 

 may be readily cut with a knife, though occasionally they are 

 rather hard, especially the sandstones. The semi-arid climate, 

 which has prevented the growth of any dense covering of pro- 

 tective vegetation, has carved the thick masses of strata 

 into the most curious and fantastic forms, known as " Bad 



FIG. 2. Butte in White River Bad Lands. 



Lands." This term is an abbreviated translation of the phrase 

 " mauvaises terres a traverser," given by the early French 

 explorers to express the extraordinarily rough and broken 

 nature of the country. It must not be supposed that all bad 

 lands are composed of White River rocks; on the contrary, we 

 find them in all of the later geological formations, from the 

 Cretaceous onward, the conditions for their formation being 

 altogether physical in character. Still, the White River Bad 

 Lands are among the most striking and peculiar of them all. 

 The outlook from any high point over these Bad Lands is a scene 

 long to be remembered; vast masses of the strata have been 

 swept away by the denuding agencies, and the harder parts 



