420 Notices of Memoirs—Dr. M. Manson on Gilaciations. 
and present glaciation. One of the broadest and most recent sum- 
maries on the subject is that of Professor T. W. Edgeworth David, 
F.R.S.1 He finds that in the following horizons the presence of 
evidences of extensive ice-action is quite firmly established :—Lower 
Cambrian, Devonian, Permo-Carboniferous, Pleistocene. 
Professor A. P. Coleman also reviews the whole subject very clearly, 
and finds four periods of extensive glaciations—(1) Lower Huronian, 
left its effects over hundreds of thousands of square miles ;* (2) Early 
Cambrian, in widely separated regions; (3) Permo-Carboniferous, for 
large parts of the world; (4) Pleistocene, very general. We there- 
fore accept, for the purposes of this discussion, that ice-action of great 
extent occurred in these periods. 
Cambrian Glacial Action—KEvidences of the action of ice in 
Cambrian time have been observed from Arctic, through north 
temperate and tropical, and in south tropical latitudes. Evidences 
of Cambrian life have been found which are of wide distribution as 
to latitudes and indicative of warm seas. ‘‘The testimony of the 
fossils, wherever gathered, implies nearly uniform climatic conditions, 
not only over our own continent, but throughout all the earth where 
records of the Cambrian Period are found.’’? The extremely wide 
range of life in Cambrian time justified Dana in saying, ‘‘ There was 
no frigid zone, and there may have been no excessively torrid zone.”’ + 
Ewidences of Glacial Action in the Devonian Era.—When the 
evidences of glacial action in the Devonian era are compared it 
is found that they embrace nearly as wide a distribution in latitude 
as do the evidences of the life of that era, and that, lke the 
distribution of temperature and of life in the preceding Silurian 
and succeeding Carboniferous era, both life and glacial action were 
distinctly non-zonal in distribution, and the former indicated warm 
temperate or tropical conditions. 
Permo- Carboniferous Ice-sheets—During Permo-Carboniferous time 
extensive sheets of ice were laid down in the tropical latitudes of 
both hemispheres. During this period the life was indicative of 
temperate conditions rather than Arctic, and its distribution was 
worldwide. ‘‘The Permian Period lies in the midst of geological 
history, with periods of great uniformity and remarkable Polar 
geniality both before and after it.” ° 
It must be recognized at once that zones of temperature did not 
prevail immediately before, during, nor immediately after the Permo- 
Carboniferous glaciation ; that whatever part solar radiation played in 
the climatic distribution of that age it was not the controlling part, as 
at present, and that to attempt to fit such a distribution of temperature 
to solar radiation involves suppositions and hypotheses which have not 
been made to harmonize with present conceptions of solar-controlled 
climates. The volcanic heat liberated at the close of this era, and that 
1 See Trans. Tenth Int. Geol. Cong., Mexico, vol. i, pp. 437-82, 1906. 
2 Bull. Geol. Soc. Am., vol. xix, pp. 847-69, November, 1908. See also Davis, 
ibid., vol. xvii, p. 414, August, 1906. 
8 Chamberlin & Salisbury, Geology, ii, p. 273. 
4 Manual, 4th ed., p. 484. 
5 Chamberlin & Salisbury, ii, p. 656. 
ee 
