LAND PLANTS AND ANIMALS. 4? 



radiata, decline, and we find the masses of dry land increase 

 in number and extent, and begin to bear an amount of forest 

 vegetation, far exceeding that of the most sheltered tropical 

 spots of the present surface. The climate, even in the latitude 

 of Baffin's Bay, was torrid ; and the atmosphere has been 

 supposed by some to have contained a larger charge of car- 

 bonic acid gas (the material of vegetation) than it now does. 

 The forests or thickets of the period included no plants speci- 

 fically the same with those now known upon earth. They 

 mainly consisted of gigantic vegetables, many of which are not 

 represented by any existing types, while others are akin to 

 kinds, which, in temperate climes at least, are now only found 

 in small and lowly forms. That these forests grew upon a 

 Polynesia, or multitude of small islands, is considered probable, 

 from similar vegetation being now found in such situations 

 within the tropics. 



With regard to the circumstances under which the masses 

 of vegetable matter were transformed into successive coal strata, 

 there have been various opinions. From examples seen at the 

 present day, at the- mouths of such rivers as the Mississippi, 

 which traverse extensive sylvan regions, and from other cir- 

 cumstances to be adverted to, it was suggested that the vege- 

 table matter, the rubbish of decayed forests, was carried by 

 rivers into estuaries, and there accumulated in vast natural 

 rafts, until it sunk to the bottom, where an overlay of sand or 

 mud would prepare it for becoming a stratum of coal. It is 

 now generally believed that the vegetation first passed into 

 the condition of a peat moss, that a subsidence then exposed 

 it to be overrun by the sea, and covered it with a layer of 

 sand or mud j that a subsequent uprise made the mud dry 

 land, and fitted it to bear a new forest, which afterwards, like 

 its predecessors, became a bed of peat j that, in short, by re- 

 petitions of this process, the alternate layers of coal, sandstone, 

 and shale, constituting the carboniferous group, were formed. 

 It is favourable to this last view that marine fossils are rarely 

 found in the body of the coal itself, though abundant in the 

 shale layers above and below it ; also that in several places 

 erect stems of trees are found with their roots still fixed in the 

 shale beds, and crossing the sandstone beds at almost right 

 angles, showing that these, at least, had not been drifted from 

 their original situations. 



The plants of the carbonigenous period have been investi- 

 gated with great care by several able naturalists, and about 



