700 



THE WONDERS OF GEOLOGY. Lect. VII 



The ducts or glands on the vessels of the coniferae may 

 often be detected, on the recently exposed surface of a block 

 of coal without any preparation whatever. Even in the 

 ashes of coal, after incineration, the spiral vessels frequently 

 remain uninjured, and form interesting microscopical 

 objects; and in the anthracite, or stone-coal of America, 

 which is a hard slate rock, the vascular tissue may be 

 rendered distinctly visible.* 



Mr. Parkinson, whose work abounds in interesting obser- 

 vations and experiments on the fossilization of vegetable 

 substances, has shown that the formation of coal has de- 

 pended upon a change, which all vegetable matter undergoes 

 when exposed to heat and moisture, under circumstances 

 that exclude the air, and prevent the escape of the more 

 volatile principles. f In this condition, a fermentation, 

 which he terms the bituminous, takes place, of which the 

 phenomenon exhibited by mow-burnt hay is a familiar 

 example. The production of sugar, and, by continuance 

 of the process, of vinegar, is effected by vegetable fermen- 

 tation in the open air. In the process of hay-making, the 



* A method has lately been discovered by Dr. Franz Schulz, by 

 which the internal vegetable structure may be more readily detected 

 in lignite, coal, anthracite, &c, than by any other previously known. It 

 consists in treating the coal to be examined with nitric acid in a 

 platinum vessel, and then evaporating the acid by a moderate heat, 

 and igniting the residue till no further empyreumatic vapours are 

 given off; the residue is submitted to the action of nitric acid, and the 

 ignition repeated. Thus prepared, the coal is placed in a platinum 

 crucible with a lid perforated in the centre, and air is blown from a 

 gasometer through the aperture in the lid, while the crucible is kept 

 at a red heat over a spirit-lamp, so that the coal is slowly consumed. 

 The ash thus obtained is not in the state of coke, as would be the case 

 in the ordinary method of incineration, hut forms a brown powder 

 full of white splinters. These splinters, on microscopical examination, 

 are found to be the siliceous cellular structure of the original vege- 

 table. By this process vegetable tissue has been detected in the 

 anthracite, or stone-coal of Pennsylvania, by Dr. Baily. — Sec A mcrican 

 Journal of Science, vol. i. 2d series, p. 124. January, 1846. 



f Organic Remains of a Former World, vol. i. p. 181. 



