September 2, 1898.] 



SCIENCE. 



287 



another the cooler uplands, while already 

 erhaps a few forms became adapted to the 

 more arid desert areas, as is the case now in 

 Australia, which is in a sense a Mesozoic 

 continent. 



Similar subsidences and elevations 

 changed the Jurassic map in Eurasia. 

 This continent was already a land mass of 

 great extent, and fresh-water lakes ex- 

 tended across Siberia, and in China were 

 extensive swamps and submerged lands, 

 now represented by coal fields. Afterwards 

 in the middle Jura this continent subsided, 

 and the Jurassic sea covered the greater 

 part of Europe and Asia, this being, ac- 

 cording to Neumayr, ' one of the greatest 

 transgressions of the sea in all recorded 

 geological history.' Subsidences and ele- 

 vations resulted, it is supposed, in cutting 

 off India from Eurasia, so that the strait or 

 sea covered the site of the Himalayas, and 

 India was possibly joined to Australia, the 

 Malaysian peninsula forming the connect- 

 ing link ; or perhaps it stretched to the 

 southwestward and was joined to South 

 Africa. However this may be, it is suffi- 

 cient for our present purpose that these vast 

 changes in the relative position of land and 

 sea were productive of a corresponding 

 amount of variation and perhaps of immi- 

 gration and consequent isolation. At all 

 events, throughout the Jurassic seas as a 

 whole there seemed to have been remarkable 

 faunal differences. This led ISTeumayr, in 

 which he is followed by Kayser,* to con- 

 ceive that there were already in Jurassic 

 times climatic zones corresponding to the 

 boreal, polar, north and south temperate 

 and tropical zones of the present day. If, 

 however, with Scott, we reject this view 

 and substitute for it the supposition that 

 ' the marked faunal differences are due to 

 varying facies, depth of water, character of 

 bottom, etc., and even more to the partly 



*Text-book of Comparative Geology, translated 

 and edited by Philip Lake, p. 270, 271. 



isolated sea-basins and the changing con- 

 nections which were established between 

 them,' it is of nearly the same import to the 

 geological biologist, for these varying con- 

 ditions of the Jurassic ocean bottom could 

 not have been without their influence in 

 causing variation, modification and adapta- 

 tion to this or that set of conditions of ex- 

 istence. 



Turning now to the effects of the Appa- 

 lachian revolution on the life of that time 

 we see that the biological results were, in 

 the main, in conformity with the geological 

 changes. During the Carboniferous period 

 vertebrates with limbs and lungs appeared, 

 i. 6., the labyrinthodonts or Stegocephala. 

 They were, compared with the other orders 

 of their class, the most composite and highly 

 organized of the Amphibia. 



Throughout the long period of compara- 

 tive geological quiet, those long ages of 

 preparation which ended in the crisis or 

 cataclysm which closed the Paleozoic, the 

 amphibian type was slowly being evolved 

 in the swamps and bayous of the lowlands 

 of the Devonian, whose vegetation so nearly 

 anticipated that of the Carboniferous from 

 some Devonian* or late Silurian ganoids, 

 from which diverged on the one hand Dip- 

 terus and the colossal lung- fish (Diniohthys 

 and Titanichthys, of the Devonian, and per- 

 haps on the other the labyrinthodonts, which 

 may have sprung from some crossopterygiaa 

 fish like Polypterus, and whose pectoral and 

 ventral fins became adapted for terrestrial 

 locomotion. The type was evidently 

 brought into being provoked by, and at the 

 same time favored by, the great extent of 

 low coastal swampy land and bodies of 

 fresh water which bordered the Atlantic 

 seaboard from the Silurian time on. 



How the amphibian type arose from the 

 ganoid stock is a matter of conjecture. It 



* Certain footprints recently discovered in the upper 

 Devonian show that the type had become established, 

 at least vertebrates with legs and toes. 



