THE DATE OP THE GLACIAL PERIOD. 351 



are almost unmodified. Intersecting streams, it is true, 

 have scored them and interrupted their continuity for 

 brief spaces ; but the beating of the rain has hardly left a 

 trace. The sea-cliffs still stand as they first stood, except 

 that frost has wrought upon their faces so as to crumble 

 away a portion and make a low talus at the base. The 

 embankments and beaches and bars are almost as perfect 

 as though the lake had left them yesterday, and many of 

 them rival in the symmetry and perfection of their con- 

 tours the most elaborate work of the engineer. There 

 are places where boulders of quartzite or other enduring 

 rock still retain the smooth, glistening surfaces which the 

 waves scoured upon them by clashing against them the 

 sands of the beach. 



" When this preservation is compared with that of the 

 lowest Tertiary rocks of the region — the Pliocene beds to 

 which King has given the name Humboldt — the differ- 

 ence is most impressive. The Pliocene shore-lines have 

 disappeared. 



" The deposits are so indurated as to serve for building- 

 stone. They have been upturned in many places by the 

 uplifting of mountains. Elsewhere they have been divided 

 by faults, and the fragments, dissevered from their contin- 

 uation in the valley, have been carried high up on the 

 mountain-flanks, where erosion has carved them in typi- 

 cal mountain forms. . . . The date of the Bonneville 

 flood is the geologic yesterday, and, calling it yesterday, we 

 may without exaggeration refer the Pliocene of Utah to 

 the last decade; the Eocene of the Colorado basin to the 

 last century, and relegate the laying of the Potsdam sand- 

 stone to prehistoric times." * 



Mr. Eussell adds to this class of evidence that of the 

 small extent to which the glacial striae have been effaced 



* Second Annual Report of the United States Geological Survey, 

 p. 188. 



