FOSSIL PLANTS. 



657 



varieties wliicli go under tlie name of cannel, 

 parrot, and splint coal, tlic crystalline stmcture, 

 so conspicuous in fine caking coal, is ivliolly 

 wanting. The first kind of cells are rarely seen, 

 and the whole surface displays an almost uni- 

 form series of the second class of cells, filled 

 with bituminous matter, and separated from 

 each other by their fibrous divisions; and it seems 

 probable, that these cells are derived from the 

 reticular texture of the parent plant, rounded 

 and confined by the enomious pressure to which 

 the vegetable matter has been subject." In the 

 more perfectly preserved specimens of fossil coal 

 called jet, the ligneous structure is very apparent; 

 so much so, as to indicate the kind of plant to 

 wliich the coal owed its formation. The great 

 extent and thickness of the coal fields in various 

 parts of the world, show the vast quantities of 

 vegetable matter which must have gone to the 

 formation of them. Nearly one half of the sur- 

 face of the west and north west part of Eng- 

 land is composed of coal strata ; and the coal 

 fields of Newcastle cover an area of about 200 

 square miles. Besides these, there are extensive 

 coal districts in Wales, in the southern part of 

 Scotland, and in Ireland. Coal fields are also 

 found on various parts of the continent of Eu- 

 rope, in North America, in New Holland, and 

 within the arctic circles, as well as in the tropi- 

 cal parts of India. 



These coal deposits are usually formed in 

 liollow troughs, in successive layers varying in 

 thickness from a few inches, to 10 and 20 feet, 

 and alternating at various intervals with strata 

 of sandstone and clay shale. The lowennost 

 layer of the coal seam is generally composed of 

 a hard clay ironstone, with a considerable ad- 

 mixture of earthy matters, while the upper 

 layers or roof of the seam is formed of a clay 

 strata rich in impressions of fems and other coal 

 plants. From the entire state of preservation 

 in which these delicately formed plants are thus 

 found, the conclusion has been drawn, that the 

 greater number of the vegetable bodies have 

 grown on the spot, or at least very near to 

 where they are now found deposited ; while on 

 the other hand, the large rounded, branchless, and 

 imperfect trunks of trees which are not unfre- 

 quently found irregularly interspersed among 

 the coal strata, would as distinctly point out that 

 many trees and vegetables had been drifted from 

 other localities into the troughs which they now 

 occupy. 



Perhaps, if we suppose wide and extended 

 tracts of level marshy ground, interspersed with 

 lakes, through which large rivers flowed, in 

 occasionally accelerated and flooded courses into 

 the neighbouring ocean, we shall have a pretty 

 good idea of the state of the country during the 

 period when the carboniferous strata were fonn- 

 ed. We must also suppose, that various changes 



of level had taken place during this period, by 

 which the waters of the ocean sometimes en- 

 croached, and at other times retreated from the 

 flat level shores; and that finally, by volcanic 

 agencies, the whole had been broken up, and 

 elevated into the positions which the coal fields 

 at the present day present to our view. 



The principal families of plants composing the 

 coal strata, are ferns, calamites, lycopodiaccje, 

 sigillarise, stigmariie, and trees of the coniferte 

 and palm tribes. The same fossil plants, as al- 

 ready mentioned, are found throughout the 

 whole known coal fields in every region of the 

 globe; so that if we suppose these coal fields to 

 be nearly of contemporaneous origin — and of this 

 too there is strong proof, from their similar rela- 

 tive position with regard to other strata — we have 

 strong reasons for supposing that a similar tem- 

 perature, and a uniform distribution of the same 

 vegetable products, existed at that period on the 

 earth's surface. That this temperature was ap- 

 proaching to tropical, we have also reason to 

 suppose, from the nature of the vegetables, most 

 of which are allied to families which are now 

 intertropical, or natives of climates with a higher 

 temperature than that of Britain at the present 



day. 



We shall now shortly describe some of the 

 most remarkable plants of the coal series. 



Lepidodendkon, (Stemlergii.) -This is one 

 of the most common fossil plants of the coal field?. 



a I.epidodpndron, Stornbcrgii. !i c L«pidostrol)ii« 



vai-iabili». d Lepidophyllum. 



The figure represents only a portion or upper 

 branch of the plant. The rhomboidal spaces 

 with which the whole is regularly marked, were 

 the base of the leaves, which appear to have been 

 linear, lanceolate, and slightly incurved. The de- 

 pression seen a little above thecentre of the spaces, 

 was the point where the leaves were attached ; 

 and the dark line which runs from this point 

 downwards, was probably an original depression, 

 unconnected with the union of the leaf. The 

 general structure of the lepidodcndron appears 

 4 o 



