Review of Recent Geohxjicdl Literntnre. 317 
Bulletin of the Geological Society of America, the Quarterly Journal of 
the Geological Society of London, and the American Journal of Science 
are hei-e collected to give in one publication the results of his extensive 
explorations and studies in this district. With these he might well have 
included also his earlier paper on the "Discovery of the Preglacial Out- 
let of the Basin of Lake Erie into that of Lake Ontario, with notes on 
the Origin of our Lower Great Lakes," from the Proceedings of the 
American Philosophical Society (vol. xix, pp. .300-337, 1881). The chief 
outlines of the author's work, as given in these papers, have also been 
recently stated by him in the American Geologist (vol. xiv, pp. 289- 
.301, Nov., 1894). His estimate of 32,000 years as the past duration of 
the Niagara river and falls seems, however, to the present reviewer less 
in accordance with the results of many investigations bearing on the 
duration of the Ice age and of the Postglacial period, than the 7,000 
years which Gilbert estimated, with some considerations tending to in- 
crease and others to reduce the estimate, in his American Association 
paper in 1886. This question, and that of the Nipissing outlet from lake 
Algonquin, on which Prof. Spencer bases the greater part of his large 
estimate, have been considered in the American Geologist (vol. xiv, 
pp. 62-65, July, 1891), with the conclusion that the volume of the Niag- 
ara river has been nearly as now through all its history. w. u. 
Critical Periods in the History of tlie Earth. By Joseph LeConte. 
(University of California, Bulletin of the Department of Geology, vol. i, 
pp. 313-336, August, 189.5.) This paper is a more full statement of the 
conclusions presented by the author two years ago in the World's Con- 
gress of Geologists at the Columbian Exposition, on the question, "Are 
there any natural divisions of the geological record which are of world- 
wide extent?" An outline of that address was given in the Am. Geol- 
ogist for October, 1893 (vol. xii, p. 272). Critical periods, having ex- 
ceptionally rapid evolution of new species of plants and animals, so that 
they mark the limits of the great geologic eras, are shown to be pro- 
duced by exceptionally great changes in physical geography, permitting 
migrations with adaptation to new environment, and by climatic 
changes, which compel migrations along north and south courses. The 
more rapid rate of evolution gives rise to higher dominant classes, and 
the great changes brought by the dominion of man over the lower ani- 
mals and plants have led the author to name the latest and present 
grand division of geologic time the Psychozoic era. He would terminate 
Quaternary time at the end of the Glacial period, and would unite the 
Tertiary and Quaternary divisions of time as together constituting the 
Cenozoic era. By the epeirogenic movements inaugurating the Glacial 
period. North America and northern Europe were "certainly raised at 
least three thousand feet and probably much more:" and at nearly the 
same time the Sierra Nevada, Wahsatch and St. Elias ranges were 
greatly uplifted by block-tilting. 
As the Glacial period marked the limit of the Cenozoic era. so the 
Laramie period, with still grander epeirogenic and orogenic changes, 
the latter taking place especially along the Cordilleran or Rocky Moun- 
