482 THE PERMIAN PERIOD 



to re-form themselves, regenerate their species, and prepare for a 

 succeeding invasion of the continental areas. On the American 

 continent, the St. Lawrence embayment had done repeated duty 

 in this line; but there is no specific evidence that it participated 

 notably in the Permo-Triassic transition. The border of the Gulf 

 of Mexico, the Mediterranean tract, notably in the region of Sicily 

 and southeast Europe, and the Ganges-Indus tract of southern Asia, 

 seem to have been special areas of refuge and regeneration at this 

 time. Here and on the continental borders generally, the shallow- 

 water marine faunas passed from the Paleozoic to the Mesozoic 

 phases. The restriction, compared with the expansional stage of 

 the Mississippian period, was great; but the faunas emerged with 

 new species born in adversity, ready for conquest when the re- 

 advancing seas should give them an expanding realm. Unfortu- 

 nately, the sediments in which this transition of faunas should be 

 recorded are, for the most part, buried and inaccessible. 



PROBLEMS OF THE PERMIAN 



Between the marvelous deployment of glaciation, a strangely 

 dispersed deposition of salt and gypsum, an extraordinary devel- 

 opment of red beds, a decided change in terrestrial vegetation, a 

 great depletion of marine life, a remarkable shifting of geographic 

 outlines, and a pronounced stage of crustal folding, the events of 

 the Permian period constitute a climacteric combination. Each 

 of these phenomena brings its own unsolved questions, while their 

 combination presents a series of problems of g.feat difficulty. These 

 marked phenomena were probably related to one another, and their 

 explanation is quite sure to be found in a common group of co-opera- 

 tive factors. While it is too much to hope for a full explanation at 

 once, there is no occasion to blink the facts or evade the issues they 

 raise. 



It is to be noted that none of the factors in this combination is 

 wholly new to geological history. There had been glaciations al- 

 most as strange in early Cambrian times; there had been signs of 

 unusual aridity in the salt and gypsum deposits of the Silurian; 

 there had been red beds in the Devonian and Keweenawan; there 

 had been marked restrictions of life, as at the close of the Ordovician; 

 there had been extensive geographic changes in earlier Paleozoic 

 periods; and there had been foldings of surpassing intensity in 

 Archean and Proterozoic times. The peculiarity of the Permian 



