10 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 2, 



ft. in. 



Shale, grey 16 



Bituminous limestone. Modiola, Cypris, Fish-scales, Spirorbis 4 



Shale, grey 9 



Bituminous limestone. Modiola, Fish-scales, C5^pi-is 6 



Shale, grey 2 6 



Bituminous limestone and calcareo-biturainous shale. Modiola, 



Fish-scales, Cypris 3 



Shale, grey 1 6 



Calcareo-bituminous shale. Modiola, Fish-scales, Cypris, Poacites 6 



Shale, grey 6 



Bituminous limestone. Cypris, &c 3 



Shale, black 7 



Coal 6 



Bituminous limestone. Cypris, Stismaria-rootlets 2 



Coal .". 0^ 



*Underclay. Stigmaria-rootlets 4 



Shales and sandstones, red and chocolate (not measured). 



Total thickness... 2819 2 



II, Remarks on the Mineral Character and Arrangement of 

 the Beds. 



The rocks included in the foregoing section are, in the order of 

 their respective aggregate thicknesses, shales and clays, sandstones, 

 coals, and bituminous limestones. 



1 . Shales and Clatjs constitute the greater part of the total thick- 

 ness, and consist of indurated mud, more or less laminated, and 

 variously modified by contact with organic matters. Its original 

 colour may be assumed to have been the dull red or chocolate*, 

 due to the presence of peroxide of iron, and which still prevails m 

 many parts of the section ; but, where ic has been long in contact 

 vsdth decomposing vegetable matter, it has assumed various greyish 

 tints. This discoloration has been efFected in two ways: — (1.) In 

 many of the beds the peroxide of iron has been deoxidized and 

 dissolved by the agency of carbonic acid disengaged in the decay of 

 the vegetable matter ; and it now appears in the form of nodules and 

 bands of the argillaceous carbonate of iron included in the shales. 

 Modern analogies, in the case of swamps and bogs, would lead us to 

 conclude that this change occurred in fresh water. (2.) Where sea- 

 water has had access to the beds, the deoxidation of its sulphates 

 and the production of sulphuretted hydrogen have caused the 

 ferruginous colouring matter to be converted into the bisulphuret of 

 iron, which appears in lai'ge quantity in some parts of the section. 

 This change now occurs m the lower parts and subsoils of salt- 

 marshes, and may everywhere be observed in those of Nova Scotia ; 

 and it is deserving of notice that in modern marshes this chemical 

 change, which in a short time converts red mud into a dull grej'^ 

 colour, is not incompatible with the contemporary growth of Carices 

 and other marsh-plants. The frequent alternation and mixture of 



* Pull shades of chocolate-red and purplish red. 



