COMMENCEMENT OF LAND PLANTS. 49 



subsequent ages to prove of the greatest service to the 

 human race, even to the extent of favoring the progress 

 of its civilization. 



The animal remains of this era are not numerous, in 

 comparison with those which go before, or those which 

 come after. The mountain limestone, indeed deposited 

 at the commencement of it, abounds unusually in poly- 

 piaria and crinoidea ; but when we ascend to the coal-beds 

 themselves, the case is altered, and these marine remains 

 altogether disappear. We have then only a limited vari- 

 ety of conchifer and shell mollusks, with fragments of a 

 few species of fishes, and these are rarely or never found 

 in the coal seams, but in the shales alternating with them. 

 Some of the fishes are of a sauroid character, that is, par- 

 take of the nature of the lizard, a genus of the reptilla, a 

 land class of animals, so that we may be said here to have 

 the first approach to a kind of animals calculated to breathe 

 the atmosphere. Such is the Megalichthys Hibbertii, 

 found by Dr. Hibbert Ware, in a limestone bed of fresh- 

 water origin, underneath the coal at Burdiehouse, near 

 Edinburgh. Others of the same kind have been found in 

 the coal measures in Yorkshire, and in the low coal shales 

 at Manchester. This is no more than might be expected, 

 as collections of fresh water now existed, and it is presu- 

 mable that they would be peopled. The chief other fish- 

 es of the coal era are named palaeothrissum, palaeoniscus, 

 diperdus. 



Coal strata are nearly confined to the group termed the 

 carboniferous formation. Thin beds are not unknown 

 afterwards but they occur only as a rare exception. It is 

 therefore thought that the most important of the conditions 

 which allowed of so abundant a terrestrial vegetation, had 

 ceased about the time when this formation was closed. 

 The high temperature was not one of the conditions which 

 terminated, for there are evidences of it afterwards ; but 

 probably the superabundance of carbonic acid gas supposed 

 to have existed during this era was expended before its 

 close. There can be little doubt that the infusion of a 

 large dose of this gas into the atmosphere at the present 

 day would be attended by precisely the same circum- 

 stances as in the time of the carboniferous formation. 

 Land animal life would not have a place on earth ; vege- 

 tation would be enormous ; and coal strata would be form- 

 ed from the vast accumulations of woody matter, which 

 6 



