A\CENI ORY OF PROGRESS IN PALEONTOLOGY 5Ol 
tory. In fact many parallels may be drawn between this history 
of faunas and the history of the races of men. 
Those organisms which are preserved in the sedimentary 
rocks, and among which our historical investigations may be car- 
ried on, are to a large extent the marine organisms which inhab- 
ited the shallow seas which have existed in past time upon the 
continental platforms, both on the borders and in the interiors of 
the continents. The life of the dry land, that of the fresh 
waters, and the aérial life, cannot have been preserved except 
under exceptional conditions. The ancient life of the abysmal 
depths of the oceans is unknown to us because of the entire, or 
at least approximate, absence of abysmal sedimentary deposits 
upon the continents. 
Among the earlier geologists of the century, whose indi- 
vidual observations were limited to comparatively small geo- 
graphic areas, at a time when the literature of geology and 
paleontology was but limited, the notion grew up that identity 
of fossil species and identity of age of the strata containing the 
fossils always went together. But gradually, with the increas- 
ing knowledge of living marine organisms, especially of their 
geographic distribution into more or less distinct provinces 
limited by physical conditions such as temperature, depth, ocean 
currents, purity of water, etc., and with the broadening knowl- 
edge of fossils themselves, when it came to be realized that the 
same organisms did not live everywhere at the same time in the 
past, but that, as now, there were also during all geologic time 
distinct zodlogic provinces inhabited by distinct faunas, and, fur- 
thermore, that these provinces were constantly changing their 
geographic boundaries, then the task of accurate or even 
approximate correlation of strata over any great distances from 
their fossil contents seemed to become almost hopeless. Indeed, 
so hopeless did the task seem to some that in 1862, in his pres- 
idential address before the Geological Society of London, Hux- 
ley’ said: ‘‘ For anything that geology or paleontology are able 
to show to the contrary, a Devonian fauna and flora in the British 
1@, 1..G. S\, Vol. XVII, p..46: 
