36 THEEE GEOLOGICAL PROVINCES. 



not carried away to the sea but was deposited in fresh water basins. But 

 at last these fresh water basins themselves were drained and their beds 

 faulted and flexed and eroded, and their sites are now found marked by 

 broad stretches of bad-lands. 



I speak of an open sea to the east of the Park Mountains, where now 

 the Great Plains stretch in broad expanse. That there was a sea or arm of 

 the sea here is manifest, for I have collected marine Tertiary fossils of 

 Vicksburgh types in several places east of Denver; but from my exceed- 

 ingly brief studies in that region, merely as a passing traveler, I can only 

 say that the region, though simple in its topographic features, is indeed 

 complex in its geological structure. 



Throughout this great area, from the eastern slope of the Park Moun- 

 tains on the east to the eastern slope of the Sierra Nevada on the west, and 

 from the sources of the Green and Shoshoni Rivers on the north to the 

 San Francisco Mountains on the south, the whole region is broken, flexed, 

 and contorted along innumerable lines. But the great structure lines have 

 a north and south trend ; the ranges of the Basin Province run from north 

 to south ; the great faults of the Plateau Province also run north and south, 

 and the Park Ranges have a north and south trend. But these general 

 outlines are broken by oblique and transverse displacements, usually of a 

 minor magnitude, though in some cases, as in the Uinta Mountains, these 

 transverse displacements assume as great proportions as the north and south 

 flexures and faults. While the whole region is exceedingly complex by 

 displacement, it is also exceedingly complex by reason of the unconformity 

 of its sedimentary beds. And all this complexity is greatly increased by 

 reason of the floods of lava which have been poured out here and there 

 over the entire area, and now and then through Cenozoic up to the present 

 time. And all these floods of lava, all these, thousands of eruptive moun- 

 tains, thousands of mesa sheets, thousands of volcanic cones, testify to a 

 period of great volcanic activity while the region was in fact a great conti- 

 nental area, thus contradicting the generalization which has obtained in some 

 quarters that volcanic activity is adjacent to the sea. And further, very 

 much of this volcanic activity has been exhibited since the desiccation of 

 the lakes. 



