392 HISTORICAL GEOLOGY 



Folding a slow process. It is probable that the folding 

 was accomplished very slowly, as are the larger earth move- 

 ments of the present time. The anticlines probably rose so 

 gradually that the decay of the rocks and the work of streams 

 partially kept pace with the growth, so that the young moun- 

 tains were at all times ragged and gashed with valleys. This 

 is true of growing mountains to-day, such as the Coast Range 

 of California and the St. Elias chain in Alaska, and it is safe 

 to judge the Permian by the present. Even the great thrust 

 faults, along which massive limestones have been pushed 

 several miles over younger beds, were doubtless made by a 

 succession of slippings, each advancing not more than a few 

 feet, and each slip separated from the next one perhaps by 

 months or years of time. While recognizing, however, that 

 the folding and the uplift were very slow, we may well imagine 

 the first Appalachian and Ouachita (Oklahoma) Mountains 

 as a series of lofty, rugged ranges comparable to the Alps, or 

 to the modern Pacific ranges in North America. 



Effects of expanding the continents. --The widespread 

 emergence of the continents into dry land must have produced 

 important changes, not only in the geography of the period, 

 but in the conditions of life for plants and animals, and even 

 in the condition of the atmosphere and in the climate. It will 

 be best to inquire into these matters separately. 



Adversities inflicted on the sea life. During the Paleo- 

 zoic era the shallow epicontinental seas had harbored abun- 

 dant marine animals and plants. With the exclusion of these 

 broad sheets of water from the continents the home of such 

 forms of life was much reduced in size. It would be entirely 

 natural to expect that as a result the competition for a living 

 would become much keener, and that many of the forms less 

 able to adapt themselves to the new conditions would be 

 exterminated. This may be the explanation of the well- 

 known fact that very few of the distinctly Paleozoic fossils 

 pass on into the Triassic system. Few of the large groups 

 entirely disappeared, although some were much diminished, 



