SUBSIDENCES. 13 



period. In other words, the lake contracted its area from south to north 

 during at least the latter half of the Eocene, and at the close of that age 

 finally disappeared. 



SUBSIDEKCE OF CKETACEOUS-EOCENE SEDIMENTS. 



A most interesting but perplexing problem is suggested when we con- 

 sider the enormous bulk of the Cretaceous-Eocene strata of the Plateau 

 Province and the peculiar circumstances under which they were deposited. 

 The whole series abounds in coal and carbonaceous shales, and remains of 

 land plants are abundant, even where carbonaceous matter is absent. If 

 current theories of the formation of coal are not radically wrong, we seem 

 compelled to believe that throughout that vast stretch of time which 

 extended from the base of the Cretaceous to the summit of the Eocene the 

 whole province, with the exception of a few possible but unknown land areas, 

 maintained its level almost even with that of the ocean, "^llie Dakota sand- 

 stone could not have been deposited here much if any below that level, 

 nor the Wasatch beds much if any above it. And yet we have the paradox 

 that 6,000 to 15,000 feet of strata were deposited over an area of more than 

 100,000 square miles with comparatively few unconformities and contem- 

 porary disturbances, while the level of the uppermost stratum always 

 remained at sensibl}' the same geographical horizon! 



It is incredible that the Cretaceous ocean at the commencement of 

 that age could have had a depth equal to the thickness of the strata and 

 that the sediments filled it up. The facts are wholly against sxich a sup- 

 position, and point clearly to shallow waters. The only conclusion which 

 appears tenable is that the strata sank as rapidly as they were deposited. 

 The case is analogous to that of the Appalachians during Palaeozoic time, 

 and especially during the Carboniferous ; and the more we reflect upon the 

 similarity the stronger does it become. It fails, however, when we come 

 to consider the phenomena presented in the two regions in the period sub- 

 sequent to the deposition; the Appalachian strata were flexed and plicated 

 to an extreme degree, while those of the west are for the most part calm 

 and even. Only in the vicinity of the mountains and shore lines do we find 

 them much disturbed. 



