THE FIRST AIR-BREATHERS. i6r 



imprisoned reptiles had wearily wandered round and round, in 

 the vain search for means of exit, till they died of exhaustion 

 and famine. The bones of these dead reptiles, shells of land- 

 snails and crusts of millepedes, accumulated in these natural 

 coffins, and became mixed with vegetable debris falling into 

 them, and with thin layers of mud washed in by the rains; and 

 this process continued so long that a layer of six inches to a 

 foot in thickness, full of bones, was sometimes produced. At 

 length a new change supervened, the area was again inundaud 

 and drifted over with sand, and the hollow trunk was filled to 

 the top and buried under many feet of sediment, never to be 

 re-opened till, after the whole had been hardened into sand- 

 stone and elevated to form a part of the modern coast, when 



\'u:. r-inrr.— Section of b.isc of erect Sigillaria, containing remains of land animals. 



n^ Mineral charcoal. /-, Dark-coloured s.anilstone, with plants, Lxnes, etc. c, (Iray 

 sandstone, with Calaniites and Cordaites. 



the old tree and its forest companions which had shared the 

 same fate with it, are made to yield up their treasures to the 

 gc'ologist. This history is no fancy picture. It represents the 

 results of long and careful study of the beds holding these erect 

 trees, and of the laborious extraction of great numbers of t'^em 

 and the breaking-up of their contents into thin flakes, to be 

 carefully examined wi'h the lens under a bright light in search 

 of the relics they con tamed. Fig. 1 1 in Chap. I. represents 

 the extraction of one of these trees, which happened to be 

 partially exposed by the wasung of the cliff; but many others 

 had to be laboriously mined out of the rock by blasting with 

 gunpowder. 



It is evident that the combination of circumstances referred to 



M 



