OF THE EASTERN BORDERS. 311 



The Changes which Coal has undergone, and the Conditions of the 

 Era during which it tvas deposited. 



So great is the difference between a Plant and Coal, that it may 

 naturally be inquired, what causes have operated to transform the 

 green living vegetable into a black stone ? We must endeavour to 

 connect the two extremes. 



And first the question occurs, was coal derived from plants, trans- 

 ported from a distance, and deposited in lakes and estuaries, as drift- 

 timber is at present carried by the American rivers into the Mexican 

 Gulf and the estuary of the Amazon 1 or from plants which grew on 

 places where coal-beds now exist ? To the drift hypothesis there are 

 strong objections. Humboldt calculates that the carbon produced by 

 the trees of the temperate zone, growing over a certain area, would 

 not, in one hundred years, form a stratum of more than ^g^ths of an 

 inch in thickness, and yet some coal-beds are 30 feet thick. But, 

 reasoning from the action of causes at present operating, we cannot 

 infer that the drifting process could accumulate the vast quantity of 

 carbonaceous matter required, without intermingling with it more 

 sand and mud than are found in any coal-seam. The extended area 

 of many coal-beds offers a still more serious objection. The Newcastle 

 coal-field itself has an area of 200 square miles ; but, even though 

 it were imagined that all this extent had been formed of masses 

 of drifted vegetables, it is, however, in the highest degree improbable 

 that this process could have distributed vegetable matter evenly over 

 an area of 14,000 square miles, — the area of the Pittsburgh coal- 

 seam in North America. 



Some few coal-beds, of limited extent, may have been formed of 

 drifted vegetables. There are, however, sufficient grounds for 

 affirming that, wherever a coal-bed is persistent over a considerable 

 area, it has been formed of plants which grew on the spot, and which, 

 in consequence of change of level, were subsequently covered over 

 with detrital depositions out of water. The condition of many delicate 

 fossil plants shows that they have not been brought from any great 

 distance ; but more conclusive evidence of our position is aiforded by 

 the numerous cases which have been observed, of fossil trees with 

 their roots, standing perpendicular to the slope of the strata, and on 

 the sjjot where they originally grew. In the Newcastle coal-field, 

 Sigillarise have been found resting on a small seam of coal, passing 

 through sandstone, and at length truncated, and lost in the high 

 main seam. Railway cuttings have exposed remains in situ of ancient 

 Carboniferous forests. At Dixonfold, in Lancashire, five large 

 Sigillarise were laid bare, all standing vertical to the plane of stratifi- 

 cation, and with their roots extending into a soft shale ; one of them 

 was 11 feet high and \o\ feet in circumference at the base. Near 

 to Chesterfield, above forty fossil trees were discovered in the same 

 position, standing about 3 feet apart upon a coal-bed, but with no 

 traces of roots, the stems disappeai'ing at the point of contact with 

 the coal, to form which, the root and lower portion of the stems had 

 contributed. The most interesting example in England is that at 



