ENE AE VP LO. PRAME A WORKING HYPOTHESIS 
OF SHE sCAUSE OF GLACIAL, PERIODS, ON AN 
ATMOSPHERIC: BASIS 
(Continued) 
SPECIAL APPLICATION OF THE HYPOTHESIS. TO THE KNOWN 
GLACIAL PERIODS 
Ir now remains to specifically apply the hypothesis to the 
recognized glacial periods. At present only those at the close 
of the Paleozoic and Cenozoic eras are sufficiently determined to 
require discussion. 
The mapping of the Pleistocene glacial deposits is sufficiently 
complete to show their great features, and reveals a strong 
development in the northern hemisphere, and at the same time 
a quite peculiar localization. The analysis of the deposits has 
progressed far enough to show that the glacial period was 
marked by pronounced oscillations of both the major and the 
minor kind. Interglacial epochs of a declared character may be 
assumed to be fairly demonstrated, while the glacial epochs 
themselves were attended by rhythmical stages of progress, as 
most pointedly brought out by recent detailed field work in the 
Mississippi and St. Lawrence valleys, notably that of Mr. Leve- 
rett and of Mr. Taylor. These rhythmical features are made the 
subject of a special discussion by Mr. Taylor in a paper entitled 
‘“Moraines. of _Recession and their Significance in ‘Glacial 
liheory. = 
To be really applicable to Pleistocene glaciation a working 
hypothesis must therefore not only postulate agencies capable 
of producing a glaciation covering the American plains down to 
JOUR. GEOL., VolvV., No: '5, 1807; pp. 421-405. See also “The Great: Ice= 
Dams of Lakes Maumee, Whittlesey, and Warren,” American Geologist, Vol. 
XXIV, No. 1, July 1899, pp. 6-38, and the review of this paper by MR. GILBERT in 
the last number of the Jour. GEOL. 
667 
