268 WALKS AND TALKS. 



/ unconformably on the eroded Eozoic surface which had sunken. 

 ! East of the basin continent, the new sediments were spread 

 conformably on the last Carboniferous sheets. At the close 

 of the Jurassic Age, these sediments had attained on the west, 

 a thickness of twenty thousand feet. On the east, they were 

 less than four thousand feet. 



Now rose the vast crumpled folds of the Sierra Nevada, 

 adding two hundred miles to the Basin continent on the wst, 

 and stretching southward at least to the thirty-sixth parallel, 

 and northward to Alaska. East of the Wahsatch, however, 

 every thing still remained quiet save that the great orographic 

 event of the west sent its rock-fragments, pebbles and sands 

 eastward over the ocean's floor as far as Kansas, forming the 

 conglomeritic Dakota Group at the base of the Cretaceous. 



No further orographic disturbances took place until the 

 close of the Cretaceous. To this epoch, the sedimentary sheets 

 had been laid down in conformable positions continuously 

 from the Cambrian upward. Now, however, came the turn 

 of the region at present known as the "Plateau Province." 

 Upward and undulatory movements were experienced from 

 the region of the Great Plains to the base of the Wahsatch. 

 Now rose the broad, flat, east-and-west anticlinal known as 

 the Uinta Mountains; and the whole mass on the east was 

 further upraised, of which the rocky Mountains are the salient 

 ridges. The broad shallow basin of the Colorado River was 

 now defined. On the Pacific coast, this disturbance was felt 

 only in the defining of the position of the Coast Ranges. 



The great feature of this post-Cretaceous movement was 

 the re-emergence of that part of the ancient Cordilleran area, 

 now called the Plateau Province. It had sunken, with tin- 

 whole breadth of the Cordilleran Land, at the end of the 

 Eozoic jEon. Now the two limbs of the American continent 

 were joined together. From Middle California to Boston Hay 

 was a continuous land connection. Only a narrow border re- 

 mained to be added around the Atlantic, Pacific, and Gulf 

 coasts. Remnants, however, of the ancient mediterranean sea 

 remained in the interior, forming lakes as large as Superior. 



