ON COAL. 133 



slowly accumulated at the bottom of ancient peat swamps, tlie purity 

 of the coal is completely accounted for. But if, on the contrary, it is 

 formed by the accumulation of timber carried down to the mouths of 

 great rivers during freshets, it should always be largely mised with 

 mud. 



2d. The fine preservation of the tenderest and most delicate parts 

 of plants. We have already spoken of the profusion of finely- 

 preserved leaves and entire fronds of ferns in the black slate overlying 

 a coal seam. So perfect is this preservation that large and complex 

 fronds are often entirely unbroken, and even the minutest variation 

 of the leaves as distinct as in the living fern. This fine preservation 

 of tender parts seems strongly to indicate that these leaves had fallen 

 gently from the parent stem, and been preserved on the spot where 

 they fell. It seems utterly inconsistent with the violent action of 

 currents bearing rafts to great distances. 



3d. The position of the finely-preserved leaves, &c., always on the 

 opper surface of the coal seam, (roof of the coal mine.) Precisely 

 the same is observed in every peat swamp. The perfect leaves are to 

 be found only on top, for the plain reason that these are the last 

 fallen, and therefore not yet disorganized. But in the case of accu- 

 mulations of vegetable matter at the mouths of rivers, there seems to 

 be no reason why leaves should not be entangled in all parts alike. 



4th. Coal, like peat, is composed of completely disorganized carbo- 

 naceous matter, containing fragments in which vegetable structure is 

 more distinct. This is not inconsistent with what I have already 

 said in my last lecture of the vegetable origin of even the most 

 structureless coal being detectable by the microscope. Plants are 

 composed entirely of cells. Both in peat and in coal these cells are 

 generally separated from one another. The vegetable structure is 

 completely disorganized, but the separate cells still bear unmistakable 

 marks of their origin ; the organic structure is gone, but the organic 

 origin is still visible. But if a coal seam was an imbedded raft, it 

 should be composed almost entirely of fragments of trunks, branches, 

 &c., instead of a structureless mass containing only a few such 

 fragments. 



5th. It will be recollected that a seam of coal is overlaid by black 

 slate and underlaid by fire-clay. In the black slate, as already said, 

 are found the finest impressions of leaves and other tender parts ; in 

 the Jire-day, which underlies the coal seam, are found imbedded in 

 the greatest abundance the roots of plants, and not unfrequently the 

 stumps of trees with the roots attached, precisely as they grow. And, 

 what is still more remarkable and significant, trunks of trees are not 

 unfrequently found almost entire, standing erect, with their roots still 

 bedded in the fire-clay, their trunks passing through the seam, and 

 far into the overlying strata of shale and limestone. By means of 

 evidence of this kind Lyell and Dawson have been able to make out 

 distinctly nearly 60 planes of successive vegetation in the coal field of 

 Nova Scotia. In many of these, viz: about 20, the trees are slill in 

 the position in which they grew, as shown in figure 12 ; of the rest 

 the evidence consisted in the imbedded stigmaria or roots of sigil- 

 laria. 



