A JTEW rLOEA OF 



III. CARBONIFEROUS SYSTEM. 



The Carboniferous system occupies fully three -fourths of the 

 district, and has a thickness of about 7000 feet. It is divisible 

 into four distinct formations, all of which are conformable to 

 each other, and marked by the occurrence of Stigmaria ficoides. 



1. Tuedian group or formation I applied, in 1856, to a series 

 of beds, intermediate between the Mountain Limestone and the 

 Upper Old Bed Sandstone, having an aggregate thickness of about 

 1000 feet, and consisting of grey, greenish, and lilac shales, thin 

 beds of argillaceous and cherty limestones, a few buff magnesian 

 limestones, and of sandstones and slaty sandstones, several of 

 which are red, and some, near the bottom of the series, of consi- 

 derable thickness. Several, too, of the shales and sandstones are 

 calcareous ; so that, though the limestones are thin and impure, 

 there is a considerable quantity of calcareous matter diifused 

 throughout the formation. The limestones are too imj)ure to 

 burn into lime, excepting a cui'ious bed of magnesian limestone, 

 near Carham, which is composed of carbonate of magnesia 44', 

 carbonate of lime 49'6, silica 4*, and peroxide of iron 1'2, alu- 

 mina 1 • ; and in this are nodules of red and grey chert, analogous 

 to flints in chalk. Stigmaria ficoides, Lepidodendra, coniferous 

 trees, reed-like stems on which are Spirorbis, a Sphenopteris, 

 and other carboniferous plants, occur both in the sandstones and 

 shales; but there are no beds of coal. The Fauna generally 

 consists of Rhizodus Hillerti, Gyracanthus, and other fish ; and 

 of moUusks allied to Modiola. Presh-water or lacustrine con- 

 ditions are generally indicated; for few distinct marine organisms 

 appear, and where discovered were accompanied by plants in a 

 fragmentary condition, which seem to have been swept into a 

 shallow estuary. One bed of shale, with irregular layers of 

 impure limestone, contains broken trunks of Finns primceva and 

 antiqua, showing internal structure, and associated with Ortho- 

 ceras muUiseptum (n.s.), Murohisonia Verneuliana, Pleurotomaria, 

 and a few other marine forms. Brachiopods and Encrinites, 

 which are so abundant in the Mountain Limestone, are almost 



