202 SUPfLEMENTAET NOTES. 



Lepidodendra were lofty trees, with spreading branches, which therefore required wide bases for 

 support, may we not conclude that Sigillarise of the species described were, on the contrary, trees 

 of low stature, without heavy branches?" 



I cannot quit this subject without again adverting to the remarkable phenomenon mentioned 

 In a previous note, namely, that in the bed of pulverulent earth — the under-day — on which the 

 coal invariably reposes, the roots (or Stigmarias) of large trees are generally the only organic 

 remains met with. The constant occurrence of these fossils in the under-clay, and their rarity in 

 the coal and shale, was long ago pointed out by Mr. Martin, Dr. MaccuUoch, and other geologists; 

 but the importance of the fact was not appreciated till Mr. Logan drew attention to it. In the 

 Welsh coal-field, through a depth of 1,200 feet, there are sixty beds of coal, each of which lies on 

 a stratum of clay abounding in Stigmarise. In the Appalachian coal formation of the United 

 States, the same phenomena occur. 



Thus it appears that the under-clay is the natural soil in which the roots {Stigmarice) of the 

 Sigillarife and Lepidodendra grew ; the coal above it is composed of the carbonized stems and 

 foliage of those trees ; and the roof or coal-shale is formed by the leaves and branches of a forest 

 overwhelmed and buried beneath the transported detritus of distant rocks. These phenomena may 

 be explained by supposing that a plain, densely clothed with a luxuriant intertropical vegetation, 

 was either inundated by an irruption of the sea, or overwhelmed by a flood, from the sudden 

 breaking up of the barrier of an inland lake ; or by the subsidence of the country on which the 

 forests grew. But when we find an uninterrupted series, in which triple deposits of this 

 character are repeated through many thousand feet, the solution of the problem is beset with 

 difficulties, which the hypothesis of repeated periodical subsidences, however ingenious, does 

 not, in my opinion, remove.' 



*9i:* Jaw of the Iguanodon. — Additional note to p. 194. — Since the preceding pages were 

 struck off, I have, through the kindness and liberality of Samuel H. Beckles, Esq., of Hastings, 

 obtained two portions of jaws from the Wealden of the Sussex Coast. One of these is a fragment 

 of the left side of the lower jaw, with six well-defined dental sockets; the other specimen 

 exhibits the position of the mature molars and the successional teeth in the upper jaw ; and 

 confirms the accuracy of the views of Dr. Melville and myself as to the ruminant character of 

 the arrangement of the dental organs in the upper and lower jaws of the Iguanodon, as described 

 in my memoir on the structure of the jaws and teeth ; Philos. Trans. 1848, p. 183. When this 

 specimen is completely developed, it will probably exhibit distinctly the relative position of the 

 germs and mature teeth, and the form of the inner alveolar parapet. 



' See Wonders of Geology, pp. 669, 718, 731. 



