NO. 6 PAST CLIMATE OF NORTH POLAR REGION KERRY 2.'/ 



nearer the equator than had been the case during the Paleozoic ; that in 

 the Jurassic, the tracheids first developed tangential pitting which 

 was at the end of the annual ring, and accompanied by storage ele- 

 ments (wood parenchyma). 



None of the statements in the foregoing paragraph are facts of 

 observation. There is no geological or paleontological evidence indi- 

 cating a progressive climatic cooling during geologic time, and the 

 Permo-Carboniferous glaciation was admittedly more extensive than 

 that of the Pleistocene. The presence or absence of growth rings 

 exhibits what nn'ght be called constitutional variations quite indepen- 

 dent of climate, not that they really are independent, but two associated 

 species under an identical climate will behave differently with respect 

 to this feature of their anatomy. Growth rings appear in some Pale- 

 ozoic woods many degrees nearer the equator than Jeffrey admits,' 

 and in marine formations deposited off low coasts so that they cannot 

 be considered to have been upland types. Several Lower Carbonifer- 

 ous examples have already been cited. The Paleozoic genus Mesoxy- 

 lon shows tangential pitting, which, according to Jeffrey, first appeared 

 in the Jurassic ; and the citation of a wood from the Triassic of 

 Arizona as an argument for the advance equatorward of cooler cli- 

 mates during the early Mesozoic is particularly disingenuous, as it 

 is perfectly clear that the growth rings in this case have nothing to do 

 with temperature, but are due to periodic lack of moisture in that 

 region, as exemplified by the contemporaneous gypsum deposits. 



Similarly in the recent elaborate work on geologic climates by Kop- 

 pen & Wegener, already alluded to, these authors offer explanations 

 to account for climates during the successive geologic periods, which 

 climates have not been proved to have ever existed. 



As I have pointed out on previous occasions, paleobotanists in 

 general have entirely lacked objective experience outside the temper- 

 ate zone, and have invariably overestimated temperatures. They have 

 been prone to use the present distribution of the fancied or real rela- 

 tives of their fossil forms as if temperature were the sole factor in the 

 environment, and have stopped with the geographic occurrence, with 

 the apparently simple trust that all lands in the equatorial zone were at 

 sea level and wet tropical. A sojourn in the Arctic climate beneath 

 the equator on the backbone of South America would do much to 

 correct this misapprehension, as would also some experience in the 

 temperate rain forests of different regions. 



I had intended to indicate current conceptions of contemporaneous 

 paleogeography on the maps showing the plant localities but have 



^ Several have been named in the preceding paragraph devoted to Mississippian 

 Arctic plants and others could be added. 



