656 GEOLOGY. 



these phenomena brings its own unsolved questions, while their combination 

 presents a plexus of problems of unparalleled difficulty. More than any other 

 period since the Proterozoic, the Permian is the period of problems. With little 

 doubt these marked phenomena were related to one another, and their eluci- 

 dation is quite sure to be found in a common group of cooperative agencies. 

 While it is too much to hope for a full elucidation at once, there is no occasion 

 to blink the facts or evade the issues they raise. 



Lest, however, we push our emphasis of these phenomena too far, let it be 

 noted that none of the factors in this combination were wholly new to geological 

 history. There had been glaciations almost as strange in early Cambrian or 

 pre-Cambrian times (Norway, China, South Africa) ; there had been signs of aridity 

 in the salt and gypsum deposits of Silurian and other early times ; there had 

 been prevalent red beds in the Old Red sandstone and in the Keweenawan; 

 there had been marked restrictions of life at the close of the Ordovician and 

 at other stages; 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 combination was its unusual 

 complexity, the extraordinary intensity of the glaciation, and the aridity. 



The chronological setting of the combination lends some advantages to its 

 study. It lies in the midst of geologic history, with periods of great uniformity 

 and remarkable polar geniality both before and after it. No appeal can be 

 taken to a supposed final refrigeration of the earth, or to any declining stage 

 or senile condition. It was an episode in the midst of a long history, with 

 every probability that it was not without predecessor and successor, though 

 these may not have been so marked. 



A portion of the phenomena were direct expressions of deformation, others 

 were seemingly close sequences of deformation, while still others may be only 

 the more remote sequences of deformation in the form of changes of atmospheric 

 and hydrospheric constitution. If the solution of these problems lies wholly 

 in terrestrial causes, it seems at present most likely to be found in the immediate 

 and ulterior consequences of deformation, as realized in physiographic changes, 

 and in the constitution and working conditions of the hydrosphere and atmos- 

 phere. Without assuming that this is necessarily so, this line of inquiry, yet 

 in its infancy, may be outlined. 



I. The Deformation. 

 The deformation at the close of the Paleozoic appears to have been typical 

 in that it involved an increase in the capacity of the oceanic basins and the with- 

 drawal into them of most of the previous epicontinental waters, while at the 

 same time the continents were rendered slightly more protuberant by being 

 mildly arched or warped throughout the larger part of their areas, and, in cer- 

 tain limited tracts, accidented by sharp folding of the external shell. So far as 

 present evidences go, the more pronounced arching and folding was felt chiefly 

 on the borders of the continents adjacent to the north Atlantic, but this apparent 

 limitation may be due to the imperfection of existing knowledge. Such Hmita- 



