82 
Sir C. Lyell, in his Second Visit to America, vol. 1, p. 286, 
says, " I found on visiting the various localities of the 
" natural coke, that it was caused by the vicinity or contact 
" of volcanic rocks, greenstone, and basalt, as in the Durham 
" coal field." 
Mr. Buddie writes, in the Transactions of the Natural 
History Society of Newcastle and Durham, vol. 1, p. 13, 
" That in some cases a cinder dyke converts the coal for 
" one hundred yards into coke or smudge coal." 
Mr. Foster, in the same work, p. 48, remarks, " That the 
" coke should be specifically heavier than the coal," but 
accounts for it " from the extreme pressure it was under 
" when the Trappean dyke changed it, and passed other 
" matters into it as the gases were driven off." 
Mr. H. D. Rogers, in his work on the Geology of 
Pennsylvania, vol. 2, p. 809, says, " The causes of the different 
" degrees of de-bituminisation of the coal in different parts 
" of their range, I am disposed to attribute to the prodigious 
" quantity of intensely-heated steam and gaseous matter 
" emitted through the crust of the earth, by the almost 
" infinite number of cracks and crevices which must have 
" been produced during the undulation and permanent 
" bending of the strata." 
Dr. Bevan, in the Geologist, vol. 2, p. 80, says, " I cannot 
" help imagining that the changes have been caused by trap 
" rocks, far below the surface ; and that the gradual disap- 
" pearance of the anthracitic tendency has been simply the 
" diminishing distance from the heat which has caused the 
" change north crop coal anthracitic, while the upper 
' ' measures are bituminous. I consider the reason to be that 
" the changes were subsequent to the deposition of the lower 
" measures, and prior to the upper ones." 
The authors of the Fossil Flora remark that three or four 
species of plants go to the formation of coal. One-half may 
