502 STUDIES FOR STUDENTS 
Islands may have been contemporaneous with Silurian life in 
North America and with a Carboniferous fauna and flora in 
Africa. Geographical provinces and zones may have been as 
distinctly marked in the Paleozoic epoch as at present, and 
those seemingly sudden appearances of new genera and species, 
which we ascribe to new creation, may be simply results of 
migration.” 
It was doubtless due to this seemingly more or less chaotic 
condition of the geographic distribution and the geologic range 
of fossils, that the majority of the students of extinct life during 
the latter part of the century have turned their attention to the 
biologic rather than to the geologic problems involved; but these 
very investigations which the biologists have made have mate- 
rially assisted the paleontologic geologist in his researches. The 
biologic paleontologist may, and often does, carry on his investi- 
gations and make valuable contributions with little or no knowl- 
edge of the geologic phases of the science save the more or 
less dogmatic assertions of text-books. But the paleontologic 
geologist must of necessity follow closely the results of his bio- 
logic brother, though his own investigations may be something 
entirely different. In fact, the perfection of the taxonomy of 
fossils is to the paleontologic geologist but one of the means to 
an end, and not the ultimate end sought. The two divisions of 
the science may be compared with the ancient and the modern 
methods in the study of human history. The biologic division 
may be compared with the older method of historical study, in 
which the lives of a few conspicuous characters monopolized the 
whole study. On the other hand, the investigations in paleon- 
tologic geology may be compared with the modern scientific 
study of history, in which the evolution of society is made most 
prominent, the conspicuous characters being considered as the 
results of social conditions rather than as their causes. 
At the present time it is believed by most, if not all, geolo- 
gists and paleontologists that the great geologic systems repre- 
sent practically the same time-periods throughout the world. 
It is also believed by many that the limits of the recognized 
