No. 381.] A HALF-CENTURY OF EVOLUTION. 651 
sented by coal fields. Afterwards in the Middle Jura this con- 
tinent subsided, and the Jurassic sea covered the greater part 
of Europe and Asia, this being, according to Neumayr, ‘one 
of the greatest transgressions of the sea in all recorded geo- 
logical history.” Subsidences and elevations 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 pos- 
sibly joined to Australia, the Malaysian peninsula forming the 
connecting link; or perhaps it stretched to the southwestward 
and was joined to South Africa. However this may be, it is 
sufficient for our present purpose that these vast changes in 
the relative position of land and sea were productive of a corre- 
sponding amount of variation, and perhaps of immigration and 
consequent isolation. At all events, throughout the Jurassic 
seas as a whole there seemed to have been remarkable faunal 
differences. This led Neumayr, in which he is followed by 
Kayser,! to conceive 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 isolated sea basins and the changing 
connections which were established between them,” it is of 
nearly the same import to the geological biologist, for these 
varying conditions of the Jurassic ocean bottom could not have 
been without their influence in causing variation, modification, 
and adaptation to this or that set of conditions of existence. 
Turning now to the effects of the Appalachian 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, 
t.e., 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 comparative geological quiet, 
1 Text-Book of Comparative Geology, translated and edited by Philip Lake, 
PP. 270, 271. 
