498 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



series of folds greater than any others of Paleozoic time, extending from 

 Oklahoma to Newfoundland and probably beyond. Along the Pacific 

 border the compression appears to have been slight. The continent was 

 again as large as at the beginning of the Paleozoic era, and thus it re- 

 mained nearly to the close of the Triassic, when the Pacific began to over- 

 lap the border. Along the Atlantic the continent remained emergent 

 until the latter half of the Cretacic. The slow production of cumulative 

 stresses is therefore seen until the breaking period was reached late in 

 Pennsylvanic time, the unrest lasting until the end of the Permic. This 

 was the condition of the northern Atlantic or Poseidon ocean. Of those 

 established on fossil evidence, it represents the most critical period in the 

 hiistory of the earth. 



This slow retreat of the late Paleozoic seas and the final quiet death in 

 old age of the Mississippian sea furnish the cause for the difficulty experi- 

 enced by American paleontologists in delimiting the Pennsylvanic and 

 Permic systems. The guiding faunas and the diastrophic record must 

 come from other and more equatorial lands, as these are more sensitive to 

 the pulsations of the late Paleozoic normal seas. This record is now 

 fairly well ascertained in the lands bordering the Mediterranean, which in 

 late Paleozoic time was at the bottom of the greater Tethys, 12S extending 

 from Spain to the Pacific and Indian oceans. 



SUMMARY OF EMERGENCES AND TRANSGRESSIONS 



Explanation of the table. — The appended table is a digest of the fore- 

 going descriptions of Paleozoic emergences and transgressions, to which 

 has been added the more important information of a similar character 

 concerning subsequent periods. The names of these periods or parts of 

 periods are given in the first column. 



The second column gives in percentages the amount of submergence 

 in the North American continent at the times specified, and also in 

 the area between 30° and 50° north latitude. The latter area will be re- 

 ferred to as the United States. According to the base used in plotting the 

 paleogeography, the North American continent, including Mexico, has 

 about 8,200,000 square miles, the area of the United States representing 

 about 3,530,000 square miles. 



128 "Now let us quit the coasts and examine the interior of a great continent. 



"Modern geology permits us to follow the first outlines of the history of a great ocean 

 which once stretched across parts of Eurasia. The folded and crumpled deposits of this 

 ocean stand, forth to heaven in Thibet, Himalaya, and the Alps. This ocean we desig- 

 nate by the name 'Tethys,' after the sister and consort of Oceanus. The latest successor 

 of the Tethyan Sea is the present Mediterranean." Suess : "Are ocean depths perma- 

 nent?" Natural Science, vol. 2. 1803, p. 183. 



