43 



either fall accidentally into it, or are swept from the banks by the 

 force or undermining action of the stream, and the accumulation of 

 such vegetable matter at the mouth of the larger rivers must be very 



great. 



It may be said, however, that granting this transportation of trees and 

 plants by rivers, granting their sinking to the bottom of the sea, and 

 their alternation there, in layers with beds of sand and clay, still their 

 conversion into coal has to be accounted for ; a substance uot only 

 different in appearance, but also in properties, from the substance of trees 

 and plants. Here the researches of chemical science have come to our 

 aid, for the conversion of vegetable matter into coal, has been proved by 

 the observations of Dr. MacCulloch on peat-bogs, and by a series of 

 experiments in the laboratory, institxited by that gentleman. 



Coal, freed from its adventitious earthy matter, which is merely 

 mechanically mixed with it, is resolvable into the same ultimate elements 

 as wood, and MacCulloch ascertained that the action of water on turf or 

 submerged wood, is sufficient to convert them into substances, capable 

 of yielding bitumen on distillation, and black and brittle, like those 

 varieties of coal called, by mineralogists, legnite andjel and he is further 

 of opinion, that great pressure, and long continued action, may have 

 produced the other modifications. The coal so produced, differs, however, 

 very materially in appearance and properties, as fuel, from the coal of our 

 mines, and the last link of the chain between a lump of Newcastle coal, 

 and a growing tree, is yet wanting. 



There are in England 'and Wales 12 great coal fields, but as Northum- 

 berland and Derham supply almost exclusively London, we shall 

 confine our observations to those great deposits. The length of the 

 coal field from the Tees to the Coquet, is almost 55 miles ; its greatest 

 breadth between the mouth of the Tyne and western pits, about 22 miles. 

 The coal measures are not spread horizontally over the area, but lie in 

 an inclined position, and in different parts of it. The consequence of this 

 is, that the same seams are formed at much greater depths from the 

 surface in one colliery than in another. Nor will two distant parts of 

 the field give the same sucession of strata, in a vertical section, either as 

 regards the beds of stone or the seams of coal v in point of quality and 

 thickness ; the same seam of coal swells out in one place, and in another 

 thins off so much as not to be worth the working, and the same thing 

 occurs with the sand stone and shale; a bed of stone, or seam of coal, 

 which in one pit is scarcely perceptible, will increase in another pit to 

 several feet. Neither is it to be understood that these coal strata are 



