SUBCARBONIFEROUS SYSTEM. 67 



§ 139. In Nova Scotia the lower part is called Lower Coal Measures, and the 

 upper part Lower Carboniferous Marine Formation, or more generally the whole 

 is called Lower Carboniferous, even where its thickness is 6,000 feet. It consists 

 of sandstones, shales, conglomerates, and limestones, with beds of gypsum. The 

 limestones bear Brachiopods specifically identical with those of corresponding age 

 in the Illinois basin. In Pennsylvania aud in Nova Scotia thin seams of coal 

 occur in the strata, which is not the case farther west. On Cape Breton the thick- 

 ness is 4,600 feet. In the Rocky Mountain region there is a thickness of 4,000 to 

 7,000 feet or more, and the several Groups may be determined at different places. 

 The System has been divided in the west into the Lodore Group, Tonto Group, 

 Red Wall Group, Lower Aubrey Group, and Upper Aubrey Group. Prof. Daw- 

 son found no palseontological or stratigraphical reason for regarding the Subcar- 

 boniferous as a System distinct from the Carboniferous, but as it is generally capable 

 of subdivision into Groups, is always unconformable with the Devonian, begins 

 with a sandstone, and is followed by a conglomerate or sandstone unconformable 

 with it, there is good reason for retaining the name, though if the lines were not 

 better defined elsewhere than in Nova Scotia, we might join Prof. Dawson in dis- 

 carding it. 



§ 140. There are some fossils in this System almost world-wide in distribution, 

 and belonging alike to all the Groups into which it has been subdivided ; viz. , 

 Spirifera striata, Athyris lamellosa, A. ptanosxdcata, Orihis michelini, O. resupinata, and 

 Productus semireticulatus. There are some that occur in the rocks of this age in 

 each of the Coal-basins on this continent ; as, Athyris subtilita and Productus cora. 

 It is in this Sytem at Hillsborough, New Brunswick, the bituminous mineral Al- 

 bertite is so abundant. The rocks are thin-bedded shales, composed of fine, indurated 

 clay, with much bituminous matter, and are full of fossil fishes in a good state of pres- 

 ervation. The shales have been disturbed and contorted, and contain the vein 

 of asphaltic mineral called Albertite. The theory of its creation is as follows: 

 The argillaceous mud which formed the indurated shales, was charged with finely com- 

 minuted vegetable matter, which in its decomposition furnished the petroleum that at 

 some later age escaped into a vein or fissure in the rocks, and by losing its more volatile 

 parts andjpartial oxidation , it hardened into the coaly or asphaltic substance. No extra 

 heat for such transformation was necessarily required. Springs yielding petroleum 

 flow from these rocks in various places. Peroxide of manganese, used in bleaching 

 and in gas manufacture, occurs in limestone near the base of the System, and wad 

 or black manganese ore is abundant at different places. Alum frequently occurs 

 from the spontaneous weathering of pyritous shales, and is sometimes manufactured 

 from them. Saline springs are not uncommon ; indeed, they are numerous from 

 the commencement of the Upper Silurian rocks to the close of this System, and 

 occur occasionally both above and below such range. The conglomerate on the 

 Stewiacke, Musquodoboit, and St. Mary's Rivers, is auriferous. It was formed from 

 auriferous quartz-veins, derived from the Taconic System, and gold occurs in it 

 exactly as in modern auriferous gravels, being found in the lower part of the con- 

 glomerate* and in the hollows and crevices of the underlying unconformable rocks. 

 The rocks of the age of this System in Europe are commonly known as the Mount- 

 ain Limestone. 



