DEFORMATION AND GRADATION. 301 



an increase in the rapidity of the run-off and in the velocity of the streams. 

 The direct action of gradation upon vegetation was essentially the same 

 as to-day, though it was probably more marked. It was felt chiefly in the 

 destruction of vegetation by erosion, flooding, and deposit, and in the conse- 

 quent production of bare areas for succession. It must have played a large 

 part in overwhelming and burying the coal stases of the Carbonic period, as 

 well as those of the Permian itself, and was the obvious cause of the transitions 

 from stase to strate. 



The climatic sequence. — ^The climatic changes which followed deformation 

 must have constituted a mosaic of effects due immediately to deformation, 

 circulation, and gradation. Mingled with these, and perhaps exceeding them 

 in importance from time to time, were the effects of solar changes, not unhke 

 those which are coming to be known for the present. The atmospheric conse- 

 quences of deformation are analyzed by Chamberlin andSalisbury(1906: 2 : 660) 

 in a thoroughgoing fashion. They regard the changes in the carbon-dioxid 

 content of the atmosphere, which were induced by deformation, as of primary 

 importance, and bring forward much evidence in support of this veiw. The 

 probability of the latter is somewhat reduced by recent evidence as to the 

 causes of climatic change, and its acceptance is somewhat hindered by the 

 frank statements of the authors themselves: 



"The facts that there was glaciation in low latitudes in the early Cambrian 

 or pre-Cambrian, that there was pronounced aridity in the Silurian in regions 

 where precipitation is now ample, that there had been active aerial life for 

 some time previous, and that the respiratory organs of both plants and animals 

 were strikingly similar in nature and proportions to those of recent times, 

 combine to restrain us from assuming that the atmosphere, in any of the 

 Paleozoic periods, was radically different from what it is now; but still certain 

 moderate variations are not only compatible with these facts, and all other 

 known phenomena, but seem to be required by the phenomena whose inter- 

 pretation is here sought, as well as by theoretical considerations." 



They regard the interruption of the free polar circulation of the previous 

 Carbonic periods as the first effect of the increased land area produced by de- 

 formation, as already noted. The second effect was the increase of continental 

 climates, and the intensifying of the atmospheric circulation between land and 

 sea, which further increased the vertical circulation and the loss of surface heat. 

 Mountains and other elevations due to deformation tend to check horizontal 

 circulation and to intensify vertical circidation. The third effect was a reduc- 

 tion of the average humidity. This follows from the increase of the land and 

 the decrease of the water area, and it is also indicated by the prevalence of 

 salt and gypsum deposits and of red beds. The reduced humidity increased 

 the loss of heat by radiation, and thus diminished temperatures generally. 

 Land lost heat more rapidly than water, and this must have increased the 

 differentiation of relatively dry cold continental climates, and of moist warm 

 oceanic climates, as well as the differentiation of seasons. This was attended 

 by an increase of convection, an additional loss of heat and a still further dif- 

 ferentiation. The fourth effect is assumed to be a change in the atmospheric 

 constituents, especially carbon dioxid, which led to a further loss of heat. 



The vegetational consequences of the foregoing climatic changes must have 

 been similar to those produced by the later glaciation in the Pleistocene. 



