EXPLANATION OF JOGGINS SECTION. 193 



submergence of the swamps of the last group, and their invasion by 

 sand-bearing currents. 



The next Subdivision commences with the growth of Calamites on 

 the surface of the great sand-bed hist noticed, after which there was 

 the formation of an iinderclay and coal, the latter being afterwards 

 inundated, and the plants at its surface overgrown with Sjiirorbis. 

 In the shale covering this coal, about fourteen feet above its surface, 

 is a bed with shrinkage cracks, and containing a stool of Stic/maria, 

 one of the roots of which was traced 9^ feet. Its rootlets were 

 attached, so that it can scarcely have been a drift stump ; and if now 

 in situ, it must have grown on a mud-bank alternately inundated and 

 dry, like the present salt-marshes of the Bay of Fundy, 



Fig. 36. — Section of Base of Erect Siyillaria. 



{a) Mineral charcoal. (5) Dark-coloured sandstone, with plants, bones, etc. 



(c) Gray sandstones with Calamites and Cordaites. 



Subdivision XVIII. is a scries of sandstones and shales, less perfectly 

 exposed than most other parts of the .section. Chocolate colours 

 prevail among the shales, and there are few fossils. One of the beds, 

 however, has its surface covered with casts of shrinkage cracks, such 

 as are now formed on mud left dry by the neap tides ; and there are 

 also erect Calamites in one bed and a Stigmarian underclay. 



The next group is of much greater interest, showing seven soil- 

 surlaccs, with a variety of sedimentary deposits. Two of the coals 

 in this group contain on their surfaces of deposition well-preserved 

 remains of the plants [Sigillaria, Coi'daites, etc.) which must have grown 

 on their underclays. A thick mass of sandstone and shale in the 

 centre of the group is also very curious, as it evidently represents the 

 side of a trench or gully cut by water in a series of mud-beds, and 

 then filled up with a confused mass of drift trees and sand. Above 

 this mass is an underclay, on which grew a forest, whose only 

 remains are a few inches of coaly matter (Gr. 11), made up in part 

 of flattened trunks converted into coal. This forest must have been 

 entirely destroyed by violence or decay, before the next bed, which 

 is a shale seven feet thick, was deposited. On the surface of this shale 

 grew a great brake of Calamites, which were buried under sand, in 

 such a manner that their forms and position were perfectly preserved : 

 they stand in groups in the oliif just as they grew, some of them being 

 five inches in diameter, and eight feet high ; and at that height they 



