600 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Gregory : Contributions to the paleontology and physical geology of the West 

 Indies. Quarterly Journal of the Geological Society of London, 1895, pages 

 255-310. 



Clark: Correlation papers — Eocene. Bulletin 83, U. S. Geological Survey, 

 1891. Maryland Geological Survey, Eocene, 1901 ; Miocene, 1904 ; Pliocene and 

 Pleistocene, 1906. 



Osborn and Matthew : Cenozoic mammal horizons of western North America. 

 Bulletin 361, U. S. Geological Survey, 1909. 



Arnold: The Tertiary and Quaternary Pectens of California. Professional 

 Paper 47, U. S. Geological Survey, 1906. Environment of the Tertiary faunas 

 of the Pacific coast. Journal of Geology, 1909. 



The new geologic Time Table 



On the basis of the paleogeography here presented and the diastrophism 

 postulated by these maps, two curves have been developed, showing the 

 amount in square miles of the various inundations throughout geologic 

 time since the beginning of the Cambric. The upper curve of the chart 

 (plate 101) is based on the land area of the North American continent as 

 at present emerged, which is estimated to be about 8,200,000 square miles 

 in extent. Since vast areas of the continent are not well known geologic- 

 ally, it was thought that errors might occur which would be detected were 

 another curve calculated for the region best known — that is, the United 

 States and a part of southern Canada, or the area between 30° and 50° 

 north latitude. The square mile content of this space is calculated to be 

 a little more than 3,530,000, the fluctuating inundation of which area is 

 illustrated by the .lower curve of the chart. A comparison of these two 

 curves shows that they are very much alike, but that the upper one based 

 on the greater area has the nodal points far more accentuated than the 

 lower one based on the smaller but better known area. It is therefore 

 probable that no marked errors, such as additional periods or differently 

 delimited periods, exist in regard to the North American continent. 



In the chart the vertical lines or abscissas are 80 in number, represent- 

 ing 57 different paleogeographical maps (52 are here published) and 23 

 other time divisions. These are named in the lower part of the chart, 

 and according to the present acceptance of them are grouped in periods 

 or systems and eras. For the 57 maps, the amount of inundation' is that 

 calculated from these maps, while for the other time divisions the amount 

 is estimated. In the former case the lines of the, plotted curves are drawn 

 straight, and in the second instance they are wavy. The time ratios are 

 based on Dana^s estimates somewhat changed, giving 12 to the Paleozoic,. 

 6 to the Mesozoic, and 2 to the Tertiary. The time in years is prac- 

 tically based on "Walcott's estimate of 1894 (Proceedings of the American 



