352 E. 0. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



close of the Devonian and again early in the Pennsylvanian. But of land 

 faunas and floras during the first and second of these four stages we 

 know absolutely nothing. Regarding even the third and fourth stages 

 our knowledge respecting their land faunas is very imperfect. As to the 

 long intervals that elapsed between the accessible records^ of the other 

 Paleozoic systems little indeed is known of the physical conditions that 

 prevailed on the lands of these times and nothing whatever of the prob- 

 able organisms. Much may have happened in these obscure intervals. 

 Whatever we may say concerning them, and however plausible, it may be 

 no better than pure speculation. I shall venture only a few suggestions 

 concerning climatic changes. 



CLIMATIC VARIATIONS 



Frequent alternations of warm and relatively cool climates, — Taking 

 the geological marine record, as preserved in the fossiliferous rocks from 

 the Cambrian to the Tertiary, it suggests equable, mild, almost sub- 

 tropical climates over the whole northern hemisphere in all the ages rep- 

 resented. Yet there is strong reason to believe — may we not say we 

 know? — that frigid conditions occurred at least locally at the beginning 

 of the Cambrian and again early in the Pennsylvanian.^^ Admitting 

 that there were icy ages, and considering the 5 or 6 advances and retreats 

 of the ice-sheet now recognized in the Pleistocene, is it unreasonable to 

 suggest that many other, periods of relatively low temperature occurred 

 during the ill-recorded emergent stages of the Paleozoic, Mesozoic, and 

 Cenozoic, of which we have as yet no positive information? 



The accessible marine record in the northern lands usually represents 

 only the more extreme submergent stages of the periods, therefore of ages 

 in which the lands were low. Besides, the character of the Paleozoic de- 

 posits in the higher latitudes indicates moderately moist, equable and 

 warm climates, and certainly not arid conditions. Aridity would have 

 favored torrential deposition of elastics which we know are almost insig- 

 nificant in amount there. But what about the intervening ages that have 

 left no accessible marine record in these northern areas ? 



It seems to me, that given sufficient moisture, relatively cool climates 

 with ice formation occurred wherever and whenever large and high land 



20 The assumption of locally frigid conditions in the early Pennsylvanian Is based 

 primarily on the fact that erratics of all sizes, some as much as 20 feet across and 5 or 6 

 feet thick, occur in the Caney shale of eastern Oklahoma. These were transported not 

 less than 50 miles and many probably were carried much farther. No other competent 

 means of their transportation than ice — presumably heavy shore ice — has been sug- 

 gested. 



