130 THE CARBONIFEROUS SYSTEM. 



stones are frequently reddened by the peroxide of iron, though usually 

 not of so bright a red as the New Red Sandstone, and always alternating, 

 at short intervals, with gray beds. It occupies a considerable breadth 

 in the county of Cumberland north of the Cobequid Mountains, in 

 Northern Colchester, and in Pictou. It is well exposed on the Joggins 

 coast, and on the coast of Northumberland Strait west of Pictou 

 Harbour. 



(b.) The Middle Coal Formation, or coal measures proper. — This 

 series includes the productive beds of coal, and is destitute of properly 

 marine limestones. Beds tinged with peroxide of iron are less com- 

 mon in this formation than in any of the others. Dark-coloured 

 shales and gray sandstones prevail, and there are no conglomerates. 

 Sigillario3 and Stigmarioz of many species are the most conspicuous 

 and abundant fossils ; but ferns, Cordaites, and Catamites are also 

 extremely abundant, and all the genera of Carboniferous plants are repre- 

 sented. Many beds, especially those in the vieinity of layers of coal, 

 contain minute Entomostraca, shells of the genus Anthracomya (Naia- 

 dites), Spirorbis carbonarius, and remains of ganoid and placoid fishes. 



The thickness of this formation may be estimated at 4000 feet. 

 It is largely developed in Cumberland, Pictou, and the eastern and 

 western sides of the island of Cape Breton, and it occupies a great 

 breadth in New Brunswick. 



(c.) The "Millstone-grit" Formation. — This name, though not in 

 all cases lithologically appropriate, has been borrowed from English 

 C? geology to designate the group of sandstones, shales, and conglome- 

 rates, destitute of coal, or nearly so, and with few fossil plants, which 

 underlies the coal measures. In its upper and middle part it includes 

 thick beds of coarse gray sandstone holding prostrate trunks of coni- 

 ferous trees [Dadoxylon Acadianum). In its lower part, red and 

 comparatively soft beds prevail. This formation is exposed in the 

 same localities mentioned above for the Middle Coal formation, and 

 especially in the south Joggins section, where it attains to the enor- 

 mous thickness of between 5000 and 6000 feet. 



(d.) The Lower Carboniferous Marine Formation. — The essential 

 features of this formation are thick beds of marine limestone, charac- 

 terized principally by numerous brachiopods, especially Productus 

 Cora, P. semireticulatus, Athyris subiilita, and Terebratula sufflata* 

 with other marine invertebrates. Associated with these limestones 

 are beds of gypsum, and they are enclosed hi thick deposits of sand- 

 stone, clay, and marl, of prevailing red colours. 



* See Davidson " On Lower Carboniferous Brachiopoda from Nova Scotia," Quart. 

 Journ. Geol. Soc, vol. xix. p. 158. 



