730 



THE WONDERS OF GEOLOGY. Lect. VII 



be, and has been, formed under each of these conditions ; 

 and that at different periods, and in different localities, all 

 these causes have been in operation; in some instances 

 singly, and in others in combination. That some of the 

 isolated basins of coal may be carbonized peat-bogs is not 

 improbable, considering that peat often occurs in beds, 

 including trees in an erect position, and extending over 

 extensive tracts of country ; and in modern peat -bogs 

 (ante, p. 66), layers are found having the conchoidal 

 fracture and lustrous appearance of coal : but no traces 

 of the plants which most largely contribute to modern peat 

 formations, as the Sphagnum, have been observed in the 

 ancient carboniferous deposits. 



Other coal-measures may have been accumulated in fresh- 

 water lakes, or in estuaries, as for example those of Burdie 

 House, and some of the Derbyshire and Yorkshire deposits, 

 where the coal is associated with lacustrine shells and 

 crustaceans : and the Shrewsbury coal-field, in which are 

 beds of limestone several feet thick, abounding in cyprides 

 and fresh-water shells.* 



But the carboniferous strata spread over vast areas, and 

 containing intercalations of sandstones, and limestones, with 

 marine remains in abundance, like those of Russia (ante, 

 p. 690), must have been deposited in the sea. The fact that 

 some beds of pure coal are from thirty to sixty feet in thick- 

 ness, seems inexplicable, except by the drifting of immense 

 masses of vegetable matter — whole forests — into the abyss 

 of the ocean, or into the basin of an inland sea. 



The occasional erect position of the stems, and the 

 preservation of delicate leaves, do not invalidate this 

 inference ; for in the rafts formed by the entangled floating 

 forests of the American rivers, trunks of trees frequently 

 occur upright ; and my distinguished friend, Admiral Sir 

 Edward Codrington, informed me that in the interior of 

 * Silurian System, p. 84. 



