On the Formation of Coal. Ill 



Next follows the shales, resembling a quiet deposit from 

 water, but bearing evidence of the existence of a vigorous 

 vegetation, in the numerous ferns and other plants imbedded 

 in them, and often resembling in beauty of outline, recent 

 specimens spread out on the pages of a well-kept herbarium. 

 Along with these are in many cases innumerable stumps of 

 SigillarijB, usually in an erect position, and spread over the 

 surface of the coal below, like the remnants of an ancient 

 forest in one of our peat mosses. This seems to prove that 

 these trees have grown in the coal, and it is a remarkable 

 confirmation of this opinion, that their roots, or the stigmariae, 

 are very rare in the shales, having probably been fixed in the 

 coal and mineralised with it. Along with the shale are found 

 seams and nodules of ironstone, either a deposit from water 

 charged with iron and soil, or more probably a segregation 

 of mineral matter from the mass of clays, round broken bits 

 of vegetables or other organic bodies. It thus resembles the 

 nodules of bog-iron-ore, forming in many mosses in the 

 present day. 



In the coal formation of Great Britain about three hundred 

 species of plants have been enumerated. Many of these are 

 mere fragments, probably portions of one plant, and, though 

 many new species may still be discovered, yet the number of 

 real species will perhaps rather be diminished than increased 

 by the future progress of science. These remains indicate 

 a most luxuriant vegetation, but it by no means follows that 

 it was also a varied one. In a forest we often find a very few 

 trees covering a vast area, to the entire exclusion of all others, 

 and so in the forests of the carboniferous epoch a few Sigil- 

 larise and Lepidodendrons may have sheltered a limited num- 

 ber of ferns, with no great diversity of other plants. The 

 analogy of existing nature would rather confirm this view, 

 as we see the common bracken in our own country, and a 

 species of the same genus ( Pterisesculenta) in Van Diemen's 

 Land and New Zealand, monopolising the whole soil, and ex- 

 cluding all other plants over wide areas. Ferns, too, indi- 

 cate a uniform climate, unfavourable to a variety of flower- 

 ing plants ; and Tasmania, barely 200 miles long, contains 



VOL. XLVI. NO. XCI. — JAN. 1849. M 



