188 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



would be oblique to the beds; time and environment will not coincide, and 

 to correlate widely separated groups of beds as synchronous in deposition 

 because of a similarity, even approaching identity, in the fauna or flora 

 would be a serious error. 



The condition, or better, the changing conditions, of upper Paleozoic 

 time, treated in a broad way, furnish an excellent concrete example of such 

 a migration of environment both vertically and horizontally. 



It is well known that under the influence of a major earth-movement 

 the continent of North America was uplifted in a progressive way from east 

 to west during upper Paleozoic time.^ Swamp and terrestrial conditions 

 initiated in the east advanced toward the west, displacing the marine condi- 

 tions even to the westernmost limits of the Plains Province and over the 

 southern part of the Basin Province. 



In this connection certain remarks made by Lee^ are of especial interest : 



"During much of the Carboniferous period sea water covered large portions 

 of the area now occupied by the mountains. Marine limestone of Pennsylvanian 

 age is abundant in central and northern New Mexico and in central and western 

 Colorado. It has been the belief of many geologists that open sea conditions 

 prevailed in western America during the time that the coal measures were form- 

 ing in the eastern and central parts of the continent. Statements are frequently 

 made that ' in the western part of the United States there are no coal accumula- 

 tions of this age (Pennsylvanian).^ There is unquestionably a large amount of 

 limestone of marine origin in the rocks of Pennsylvanian age in the Southern 

 Rocky Mountain Province, but there are also thin beds of coal and plant-bearing 

 sedimentary rocks which indicate lowlands and coastal swamps in Pennsylvanian 

 time. These have been found in New Mexico, near Socorro; in the mountains 

 east of Albuquerque ; near Santa Fe on the western slope of the main range ; in 

 the Pecos Valley between the mountain ranges; east of the main ranges near Las 

 Vegas; and farther to the north in the Moreno Valley. Thin beds of coal of 

 Pennsylvanian age have been reported from many places in central and western 

 Colorado and in eastern Utah, both north and south of the Uinta Range. These 

 coal beds are not thick enough to be of commercial value, but they prove that the 

 physiographic conditions of the Rocky Mountain region during the early part of 

 the Pennsylvanian epoch were not so different from those in eastern and central 

 North America as many geologists have supposed. However, later in the epoch 

 these coals were covered by the sea in which was formed the massive limestone 

 of Pennsylvanian age in New Mexico and southern Colorado, which seems to 

 indicate clear water and open sea conditions." 



^ Girty, G. H., Outlines of Geologic History, chap, vi, pp. 126-127, 1910. 

 Schuchert, Chas., Paleogeography of North America, Bull. Geol. Soc. Amer., vol. 20, 



chart of submergences and emergences and map of Lower Permian. 

 Ulrich, E. O., Revision of the Paleozoic System, Bull. Geol. Soc. Amer., vol. 22, chart on 



P- 343- 

 ^ Lee, W. T., Early Mesozoic physiography of the Southern Rocky Mountains, Smithsonian 



Miscellaneous Collections, Vol. 69, No. 4, p. 4, 1918. 

 ^ Schuchert, Chas., Textbook, p. 745. 



