32 THREE GEOLOGICAL PROVINCES. 



greatly sometimes, sometimes turned quite on edge, and even in some cases 

 reversed. One of these blocks standing on edge afforded Professor Meek 

 the opportunity to make his section on Sulphur Creek published in Dr. Hay- 

 den's Report on the Geological Survey of Montana, Idaho, Wyoming, and 

 Utah, 1872. Professor Meek evidently recognized the difficulty of correlat- 

 ing the strata in that section with those outcropping elsewhere in the dis- 

 trict. I mention these excessively complex zones without attempting to 

 explain them. Some student of geology will eventually find here a subject 

 rich in results. 



SUMMARY OUTLINE OF THE HISTORY OF THE THREE 

 PROVINCES DURING CENOZOIC TIME. 



In the latter part of Mesozoic time the greater part of the .Basin Province 

 was dry land. The Plateau Province was an open but shallow sea. In 

 the Park Province a chain of islands extended to the south. The Cenozoic 

 time was inaugurated by a series of movements, which, continued to the 

 present time, have produced the topographic features now observed. This 

 part of the crust of the earth, and I mean by the term " crust" simply that 

 portion of the earth which we are able to study by actual observation in 

 truncated folds and eroded faults this portion of the crust, then, was gradu- 

 ally broken and contorted. The Plateau and Park Provinces were cut off 

 from the sea, and great bodies of fresh water accumulated in the basins, 

 while to the east in the region of the Great Plains, in earlier Tertiary times 

 at least, there was an open sea. Slowly through Cenozoic times the outlines 

 of these lakes were changed, doubtless in two ways : first, by the gradual 

 displacement of the rock beds in upheaval and subsidence here and there ; 

 and, second, by the gradual desiccation due to the filling up of the basins by 

 sedimentation and the erosion of their barriers ; and the total result of this 

 was to steadily diminish the lacustrine area. But the movements in the dis- 

 placement extended over the Basin Province, for that region was then a 

 comparatively low plain, constituting a general base level of erosion to 

 which that region had been denuded in Mesozoic and early Tertiary time 

 when it was an area of dry land ; for I think that from the known facts we 

 may reasonably infer that the Basin Ranges, though composed of Paleozoic 



