OUTLINES OF GEOLOGY. 



55 



The vegetables belong principally to the orders of vascular, 

 cryptogamia, and monocotyledons ; and those of the first are 

 most numerous. Among them, are 14 of the family of equi- 

 setse, 130 of that of ferns, G8 of that of lycopodium. Of the 

 monocotyledons are a few palms and grasses. 



This enumeration shows, that the flora of the epoch of th< 

 coal formations must have differed in a remarkable manne 

 from that of the present day. Those vegetable familie; 

 which are now most numerous, being wholly wanting ; an< 

 those which are now rare, numerous. Another remarkabh 

 fact is ascertained by the examination of these remains 

 namely, that vegetables belonging to families which are now 

 mere herbs, attained at this epoch to the dimensions of the 

 largest trees. The most striking instance of this is to be 

 found among the ferns, which only in one instance attain the 

 character of a tree at the present day. This tree form is 

 only found, and even then of but small size, in the warmest 

 tropical climates. It may be hence inferred, that the climate 

 of the surface of the earth was extremely hot at the epoch of 

 the coal formations. It also seems to have been uniform 

 over the whole surface of the sphere. At the present day t 

 each latitude, and every different degree of elevation, has its 

 own series of plants ; and those of the two continents differ 

 from each other. But the fossil remains in the coal of Penn- 

 sylvania and England, of New Holland and Greenland, of 

 India and Melville Island, are identical with each other. 



131. The coal of this formation may be of every quality, 

 from an anthracite, containing little or no hydrogen, to that 

 which is richest in bitumen. The same stratum often con- 

 tains both anthracite and bituminous coal, the former where 

 it lies near the surface of the earth, or is traversed by dykez 

 of trap. It would therefore appear, as we shall illustrate 

 hereafter, that heat had an agency in the formation of coal 

 and that the volatile matter had escaped, wherever the su 

 perincumbent strata were not sufficient to confine it. 



