92 MONOGRAPH OF DURA DEN. 



were sustained ? These families arc nearly all extinct, or, as 

 in the ferns, and club-moss, and horse-tail tribes, a stunted, 

 pigmy race ; and faintly allied, in a few others, in the arbores- 

 cent kinds of the tropics, to the giant types of the coal age. 

 How few of us all, who are in the daily enjoyment of the bless- 

 ings, in a thousand forms, derived from our easy and abundant 

 supplies of this fuel, think of the long and singular processes by 

 which it was prepared, ages ago, in the laboratory of nature, 

 where the forests of primeval times, deprived of their watery 

 and volatile parts, but retaining all their combustible matter, 

 were stored up for our use in inexhaustible quantities, under 

 our feet, closely packed and walled in by a solid masonry of 

 rock! Twenty years have scarcely elapsed since Witham, a 

 Yorkshire gentleman, visited Edinburgh, obtained prepared 

 shces of our different coals from the late Mr. Nicol, lapidary, 

 placed them under the microscope, and revealed, for the first 

 time, in all their marvellous woody tissue, the structure and 

 composition of our combustible treasures. 



But the wonders of our coal-fields are not half exhausted by 

 these disclosures. The chemists tell us that the ironstone and 

 black-band, which are co-extensive almost with the coal in 

 geographical area, have chiefly derived their metallic properties 

 from the residue of the same plants which furnished the bitu- 

 minous compound. Much of the iron, doubtless, resulted from 

 the decomposed rocks of an anterior period, and was washed 

 down by the rivers into the basins in which the coal materials 

 were collected. Part of it likewise would be cast out in the 

 plutonic products from the innumerable volcanic foci which 

 everywhere existed in the coal-measures. But as in the 

 bog plants of the present time, which form our peat mosses, 

 so charged with solutions of iron, in like manner in the 

 exuberant vegetation of the carboniferous age, it is aflarmed, 

 that enough of the metal existed to form the ores of iron 

 with which the coal beds are everywhere accompanied. There 

 are at })resent, in Scotland alone, upwards of a hundred 



