298 Mr. Witham's Description of a Fossil Tree. 



brought to light, and leave room to believe, that these plants, are as 

 abundant in these deposits as in those higher up in the series. 



Another singularity to be accounted for is, the difference in com- 

 position of these Fossils from the surrounding medium. When we find, 

 in beds of Sandstone, vegetable forms of Vascular Cryptogamic plants 

 transmuted into a substance of a similar chemical nature, the presence of 

 the Sand, and the decay of the vegetable matter, afford an easy explana- 

 tion of the manner in which the transmutation has been effected ; but 

 when the petrifying substance is different in nature from that forming 

 the matrix of the Fossil, difficulties occur. Yet if we take the whole 

 mass or group of substances constituting any one formation, we may 

 find means of accounting for the fact in a tolerably satisfactory manner. 

 For instance, large Fossil Trees are found in the Mountain Limestone 

 groups. In this series we have abundance of Lime for our purpose, 

 and the reason why the Sandstone contains less Lime than the Fossil, 

 appears to be, that before the strata were consolidated, the Sand being 

 more incoherent than the Wood (although we must suppose the latter in 

 a decayed state), the Lime found a more easy passage through it, and 

 was not, therefore, retained in such great quantity as in the Fossil, 

 which being denser and in a state of decay, as the vegetable matter de- 

 composed, the Calcareous matter filled it up. Again, on the contrary, 

 those Fossils, found in the Coal-field proper, having the Mountain or 

 Carboniferous Limestone for its base, and the Magnesian Limestone, 

 or new Red Sandstone series, lying immediately above it, contain little 

 or no Lime, as will be seen by the different analyses hereafter to be 

 mentioned. It having been ascertained by analyses, that the Coniferce 

 of the Coal-field differ widely in composition from those found in the 

 Mountain Limestone group ; the latter containing large portions of 

 Carbonate of Lime, much Iron, and small quantities of Carbon ; the 

 former being composed almost entirely of siliceous matter, with scarcely 

 any other foreign substance ; — the conclusion to be drawn from these 

 marked differences in their component parts, becomes to the practical 

 miner of considerable importance. As in many of the sedimentary 



