9 
un example of the internal pressure, and hence the density 
of the earth, being relieved, and this to the enormous 
amount of the mountain limestone, extending as it does to the 
Arctic Circle.* I may remark that through the same open- 
ings, trap rocks, as the toadstone of Derbyshire, were emitted, 
and have become interstratified with the limestone beds, so 
as to have igneous rocks and chemically formed rocks in 
alternate succession. 
c. Passing over the milhtonc grit, we now come to the 
beds of coal, of which I shall take the description from Hugh 
Miller's "Testimony of the Rocks," p. 135 :— " That which 
" distinguishes this period/' says he, " is its gorgeous flora. 
" It was emphatically the period of plants, of herbs yielding 
" seed after their kind. In no other age did the world 
" ever witness such a flora ; the youth of the earth was 
" peculiarly a green and umbrageous youth, a youth of 
" tangled and dusky forests, of huge pines and stately 
" araucarians, of the reed-like calamite, the tall tree-fern, 
"the sculptured sigillaria, and the hirsute lepidodendron. 
" Wherever dry land, or shallow lake, or running stream 
" appeared, from where Melville Island now spreads out its 
" wastes under the star of the pole, to where the arid plains 
" of Australia lie solitary beneath the bright sun of the 
" south (and I may add of New South Wales) a rank and 
" luxuriant herbage cumbered every foot breadth of the soil, 
" and even to distant planets our earth must have shone 
" through the enveloping clouds with a green and delicate 
" ray." Again, he says, p. 151, " the American coal fields 
" have been carefully explored, and what is the result ? The 
" geologist has come to know that even the mighty forests 
* Dr. Richardson, under the command of Captain Franklin, between the 
parallels of 60 to 70 N. Lat. found a calcareous formation stretching from the 
mouth of Mackenzie River, in which were corallines, products, and 
terebratulse, the same in generic character to those of our mountain 
limestone. (Lyell, vol. I, p. 188.) 
