CLIMATOLOGY OF THE LATE PALEOZOIC 251 



overflow of large continental areas by shallow sea. The latter are the results of 

 the readjustments needed to bring the continents once more into isostatic balance, 

 involving the general lifting of the continents, especially of their borders, the expan- 

 sion of the continental areas to their utmost limits, and the renewal of rapid 



erosion. • r i. i 



"These alternations of conditions are marked by alternations of the prevalent 

 type of formation in the geological series. The uniform base-leveling corresponds 

 to widespread deposits of limestones and in its waning stages with coal foimations. 

 The periods of uplift are marked by thick barren formations, often red in color, 

 by indications of arid conditions in salt and gypsum beds, and they finally cul- 

 minate in great extension of glaciers from boreal and high mountain areas." 



C. CAUSE OF THE CLIMATIC CHANGE. 



The evidence for a slowly maturing cycle of climatic change which 

 culminated in excessive aridity in the late Permian or the Triassic has been 

 presented. The possible causes, atmospheric content, solar heat affected 

 by volcanic dust, and deformation, have been considered. The last was 

 the precipitating cause, at least the one which can be rationally tested 

 with the best hope of permanent results. The following discussion is 

 limited to that cause alone, though there can be no doubt that the others 

 very possibly were contributory. 



The continuity of the great tectonic line which includes the Paleozoic 

 Alps (Hercynian, Armorican-Variscan) of Europe and the Appalachian 

 Mountains of North America is now beyond question and the progress of 

 the movement from east to west along this line is equally well established. 

 That there were movements even in the western part of the line at an early 

 date is attested by the evidence of uplift even at its extreme western limit 

 in mid-Pennsylvanian time. Blackwelder^ gives the following statement in 

 regard to their movement: 



"Arkansan {mid-Pennsyhanian).— The folded structures underlying the moun- 

 tains of Arkansas and Oklahoma were made, as nearly as can be mferred_ from 

 current correlations, in the latter part of the Pennsylvanian period. Thus, in the 

 central Arkansas coal field the deformation followed the laying down of the lower 

 Pennsylvanian coal measures,^ but no younger strata exist there. In the Arbuckle 

 Mountains of Oklahoma it occurred after the deposition of the Caney shale (early 

 Pennsylvanian?) and before that of the Franks conglomerate (late Pennsylvanian). 

 In the Wichita Mountains still farther west in the same State, the folds had been 

 truncated before the deposition of the Oklahomian (early Permian) red beds. 

 Thus it is the conclusion of Taff^ 'that the Arbuckle uplift (= crumpling) began 

 near the middle and culminated near the close of the Pennsylvanian time, previous 

 to the deposition of the red beds. * * * 



' Blackwelder, Eliot, A Summary of the Orogenic Epochs in the Geologic History of North 

 America, Jour. Geol., vol. xxii, p. 641, 1914- 



2 Collier, A. J., The Arkansas Coal Field, U. S. Geological Survey Bull. 326, p. 24, 1907- 



3 Taff, J. A., Geology of the Arbuckle and Wichita Mountains, U. S. Geological Survey, 



Professional Paper No. 31, p. 80, 1904. 



