EXPLANATION OB JOGGINB BBCTION. 185 



bed of vegetable matter represented by two inches of coal. This 

 terrestrial surface was overflowed by water for a very long time 

 inhabited by Naiadites and t tytkere. This, it will be observed, implies 

 subsidence of a terrestrial surface and its long submergence; and I 

 may remark, once for all, that the appearances of the whole section 

 imply continuous subsidence, only occasionally interrupted by elevatory 

 movements. The bituminous limestone which marks this submer- 

 gence is again succeeded by coal, again submerged under water 

 inhabited by mollusks, ( '//there, etc. The succeeding group marks the 

 rilling of the quiet, waters tenanted by Naiadites with thick deposits 

 of clay and sand, and in one little bed, about three inches in thickness, 

 tilled with the shells of the little land-snails known as Pupa vetusta 

 and Conulus p7*iscus, it shows evidence of neighbouring woods or 

 swamps, from which some gentle stream must have drifted these little 

 shells over the muddy bottom. 



Subdivision IX. is a fine series of underclays and coals, alternating 

 with mussel-beds. It contains seven distinct soil-surfaces, the highest* 

 supporting an erect tree, which appears as a ribbed sandstone cast, 

 five feet six inches high, nine inches in diameter at the top, and fifteen 

 at the base, where the roots began to separate. This tree, being 

 harder than the enclosing beds, at the time of one of my visits stood 

 out boldly at the base of the cliff, nearly three-fourths of its diameter 

 and the bases of three of its four main roots being exposed. Five of 

 the underclays support coals, and in three instances bituminous lime- 

 stones have been converted into soils, none of which, however, support 

 coals. The last of these bituminous limestones is a very remarkable 

 bed. First, we have an underclay ; this was submerged, and Spirorbis 

 attached its little shell to the decaying trunks, which finally fell 

 prostrate, and formed a carbonaceous bottom, over which multitudes 

 of little crustaceans {Cy there) swam and crept, and on which fourteen 

 inches of calcareous and carbonaceous matter were gradually collected. 



Then this bed of organic matter was elevated into a soil, and large 

 trees, with Stigmaria roots, grew on its surface. These were buried 

 under thick beds of clay and sand, and it is in the latter that the erect 

 tree already mentioned occurs ; its roots, however, are about nine feet 

 above the surface of the limestone, and belong to a later and higher 

 terrestrial surface, which cannot be distinguished from the clay of 

 similar character above and below. 



The Xth Subdivision contains a vast thickness of sandstone and 

 shales, the latter chiefly of chocolate colours. It shows comparatively 

 meagre indications of the swamp-deposits previously in progress. 



* Included in the lower part of Subdivision X. of the section. 



N 



