78 PICTURESQUE SKETCHES 



Those parts of the great carboniferous series which 

 generally include the beds of coal consist of muddy 

 and sandy beds, alternating with one another and with 

 the coal itself. Some of them would appear to be of 

 fresh-water and some of marine origin ; and they 

 abound, for the most part, with remains of the leaves 

 of ferns and fern-like trees, together with the crushed 

 trunks of these and other trees, whose substance may 

 have contributed to form the great accumulations of 

 bituminised and other vegetable carbon obtained from 

 these strata, and well known under the name of coal. 



It is not easy to communicate such an idea of beds 

 of coal as shall enable the reader to understand clearly 

 the nature of the circumstances under which they may 

 have been deposited, and the time required for this 

 purpose. The actual total thickness of the different 

 beds in England varies considerably in different dis- 

 tricts, but appears to amount, in the Lancashire coal- 

 field, to as much as 150 feet. In North America there 

 is a coal-field of vast extent, in which there appears at 

 least as great a thickness of workable coal as in any 

 part of England ; while in Belgium and France the 

 thickness is often much less considerable, although the 

 beds thicken again still further to the east. 



But this account of the thickness of the beds gives 

 a very imperfect notion of the quantity of vegetable 

 matter required to form them ; and, on the other hand, 

 the rate of increase of vegetables, and the quantity an- 

 nually brought down by some of the great rivers, both 

 of the eastern and western continents, is beyond all 

 measure greater than is the case in our drier and colder 

 climates. The trees which, in many cases, contributed 

 largely to the formation of the coal, seem to have 



