112 Feather stonhaugWs Geological Report. 



if it constituted the surface a sufficient period of time, as we 

 see it did, to admit of successive generations of plants and 

 fresh-water mollusca growing on it, what duration of lime 

 must be allowed for the aggregate formation of the whole 

 coal measures, when each bed in its turn constituted the sur- 

 face for an undefined period ? And then what are we to think 

 of the period necessary for the deposition of all the stratified 

 portion of the earth, when the coal measures stand in so small 

 a relation to the whole ? 



This portion of the carboniferous group presents, also, the 

 singular spectacle of vegetable fossils prevailing almost to the 

 exclusion of all others, a circumstance which gives weight to 

 the vegetable origin of bituminous coal. Besides the pro- 

 fusion of vegetable fossil impressions found on the bituminous 

 shales superincumbent on the coal veins, we find the leaves 

 and stems of great varieties of plants dispersed in the slaty 

 and siliceous beds alternating with the coal, as if they had been 

 deposited at a geological epoch devoted almost exclusively to 

 the vegetation of plants. Assuming the vegetable origin of 

 coal, it appears most probable that coal veins must have been 

 furnished by plants which grew on the spot, as peats do at 

 present. In cases where plants have accumulated by being 

 swept from a distance into particular situations, as at Bovey 

 Heathfield, in Devonshire, where whole forests seem to have 

 swept off from the Dartmoor granite, and collected in a basin 

 lower down, we must expect to find them, as they are there, 

 mixed up with gravel and detritus ; but that does not occur in 

 the coal veins, they are composed of pure combustible matter, 

 although, as has been seen, they are sometimes divided by 

 argillaceous layers. If we were to endeavor to account for 

 the coal measures upon the hypothesis of plants transported 

 from more elevated and distant districts, in vain we look for 

 vestiges of such districts, lost in admiration at the changes 

 which the surface has undergone. The degree of bitumina- 

 tion belonging to the many varieties of coal, and upon which 



