li 
" coal. The coal formation in Melville Island, in north lati- 
" tude 75°, where the summer lasts but a few tceeks, I found on 
" examining a series of specimens to contain various tropical- 
" looking fossil plants, resembling those met with in the 
'* coal fields of Great Britain ; and as the same formation 
" occurs in Jamieson's Land, in N. L. 71°, it is very probable 
" that future naturalists will detect in its strata plants of a 
" similar nature. Remains of plants with tropical characters, 
" evidently in their native place of growth, under 75° N. L., 
" is a fact which naturally leads to very interesting discus- 
" sions as to the former state of climate, &c." 
Brongniart states that the study of the botany of the 
ancient coal deposits has yielded the strongest evidence pos- 
sible of an extremely hot climate; that there existed at that 
epoch Equiseta upwards of ten feet high, and five or six 
inches in diameter ; tree ferns, or plants allied to them, 40 to 
50 feet in height ; and arborescent Lycopocliaceae, 60 to 70 feet 
high ; that the development of these plants, even in the 
hottest parts of the globe, is inferior to that of the COAL 
formation. (Consid. Generales sur la Nature de la Vegeta- 
tion. Ann. des Sci. Nat., Nov., 1828.) 
To account for this extraordinary temperature of the earth 
extending within 15° or 20° of the north pole, and 35° of 
the south pole, various hypotheses, both astronomical and 
geological, have been suggested. Lyell supposes that a large 
continent formerly extended northwards to within the arctic 
circle ; but it is highly probable, if not certain, that there 
exists now a larger area of land in the northern hemisphere 
than at any former period. Professor Phillips supposes that 
the atmosphere contained a larger dose of carbonic acid, and 
the temperature was increased by subterranean heat. Cordier 
gives the results of his experiments and observations on 
the temperature of the interior of the earth, that the heat 
increases rapidly with the depth, but the increase does not 
