GEOLOGY. 47 



leaves are spread out on the stone like the dried plants jn the paper in 

 theherberiumof abotanist. In the greater proportion of fossil plants of the 

 coal measures, there is little appearance of woody matter; stems of a foot 

 and a half in diameter have- been found, with the external form perfectly 

 preserved; but having only a coating of coaly matter of inconsiderable 

 thickness, the interior part consisting of sand stone or clay, with now and 

 then some more coaly matter, in the centre, indicating, as it were, the 

 pith. But trunks of trees, in which the woody texture was preserved 

 nearly throughout the whole stem, have often been met with : they have 

 been seen in the coal mines of Westphalia sixty feet in length, and two 

 remarkable fossil trees in the coal measures have occurred in Great 

 Britain. In a bed of sand stone, near Gosforth, about five miles from 

 Newcastle, a stem was found which measured 72 feet in length, and 4 

 feet in width at its lower end, and from which it tapered gradually. It 

 was in a compressed state, as if flattened by great incumbent pressure, 

 so that the above dimensions of the width are not the true diameter of the 

 stem. There were no roots attached, but there were large knots, and 

 other places where branches appear to have been broken off. 



It is the general opinion of geologists, that our beds of coal have been 

 produced by vast quantities of plants, carried down from the land, and 

 accumulated at the bottom of the sea during the long succession of ages ; 

 the numerous alternations amounting to many hundreds, sometimes 

 thousands, of sand stones, shales, and beds of coal, proving a long dura- 

 tion of the process of deposition. The character of the vegetation indicates 

 not only a tropical, but also an insular climate; that is, the plants must 

 have grown on islands in a very moist atmosphere, and in a heat as great 

 or even greater than that of the West Indies. To account for the 

 extraordinary luxuriance of the vegetation, Brongniart a (French 

 naturalist, to whom society is indebted for most valuable and accurate 

 information upon the subject of fossil botany) has suggested that there 

 was probably a much larger proportion of carbonic acid gas in the 

 atmosphere of that period than now exists ; that gas, being one great 

 source of vegetable matter in the growth of plants. As any great 

 proportion of carbonic acid gas would render the air unfit to support 

 animal life, the absence of the remains of land quadrupeds among such 

 accumulations of terrestial plants certainly gives some countenance to 

 the conjecture. This mode of accounting for the deposition of our coal 

 beds is greatly in conformity with what must be now going forward in 

 many parts of the earth, to prepare beds of coal for distant ages. Every 

 river must carry down more or less of the trees, or other plants, which 



