Crawrorp.—On the Probability of finding Extensive Coal Deposits. 881 
theory on the subject, I take to be, that at the time of the deposition of the 
coal of the old European carboniferous formation, the earth still retained a 
great deal more of its original heat than now obtains, that, in consequence, 
dense vapours and a damp hot atmosphere prevailed, favourable to the 
growth of an extremely luxuriant vegetation, and from this accumulation of 
carbonaceous products the coal resulted. 
this theory be correct, we should expect to find the same con- 
ae. ice over both hemispheres, and I think also we might expect 
the greatest coal formations in the tropical regions. What we actually find 
is as follows :—Large areas of carboniferous paleozoic coal in the Northern 
Hemisphere, in Europe, in America, and in China; I think I may say no 
paleozoic coal within the tropics, and possibly none in the Southern 
Hemisphere. 
In Africa, so far as I know, no coal is found; in Australia, the coal is 
claimed by the Rey. W. B. Clarke to belong to the palxozoic era, while 
Professor M‘Coy asserts that it is of triassic age. As Professor M‘Coy is a 
paleontologist, and as the question is one of paleontology, prima facie we 
may assume that his view is the correct one. 
In New Zealand the coal is of upper mesozoic age, probably lower cre- 
taceous, and in South America all the coal that has been found is, I believe, 
of tertiary age, although, from the absence of books of reference, I am not 
able to speak positively as to its exact place. 
This, however, is comparatively immaterial. The question of the ex- 
istence of true paleozoic coal in the southern hemisphere lies between the 
arguments of Professor M‘Coy and of the Rev. W. B. Clarke as to the age 
of the Australian coal. 
But if we require a high temperature for the earth to form the paleozic 
coal, shall we not also require high temperatures for the formation of the 
secondary and tertiary coals ? 
We have a school of geologists who are very strong in argument in the 
present day as to the effects of cold glaciers and ice sheets covering the 
surface, not only in temperate regions, but even within the tropics. 
Now these changes of temperature from hot to cold and then to increased 
warmth are inconsistent with a theory of changes from secular cooling, 
which ought to be constant in one direction, viz., from heat to cold, and 
ought not to show capricious action from heat to cold and then to heat 
again. 
But is there not something weak in the original theory, viz., that the 
origin of the old carboniferous coal was caused by the dense vegetation of a 
period when the interior heat created dense vapours‘and a warm moist 
atmosphere, and thus produced an excess of vegetation. 
