132 THE CARBONIFEROUS SYSTEM. 



rocks are also in this region unconformable to the Carboniferous, 

 having been disturbed and altered prior to the deposition of the latter ; 

 while no want of conformity, except of the local character hereafter 

 to be noticed, occurs in the Carboniferous. Geinitz has shown 

 ("Isis," 1866) that my lower, middle, and upper coal formations 

 are equivalent to three of the zones into which he divides the coal 

 formations of Saxony. 



Conditions of Deposition of the Beds. 



It is evident that very various geographical conditions are implied 

 in the deposit of this vast thickness of sediment. The Acadia of the 

 Carboniferous period must not only have differed much from that which 

 now is, but it must have presented very different appearances in the 

 different portions of the Carboniferous time itself. 



The conditions of deposit thus implied in the mineral character and 

 fossils of the several formations above described, would appear to be 

 of three leading kinds: — (1.) The deposition of coarse sediment in 

 shallow water, with local changes leading to the alternation of clay, 

 sand, and gravel. This predominates at the beginning of the period, 

 recurs after the deposition of the marine limestones in the formation 

 of the " Millstone-grit," and again prevails in the upper coal forma- 

 tion. (2.) The growth of corals and shell-fish in deep clear water, 

 along with the precipitation of crystalline limestone and gypsum. 

 These conditions occurred during the formation of the Lower Carbon- 

 iferous limestone and its associated gypsum. (3.) The deposition of 

 fine sediment, and the accumulation of vegetable matter in beds of coal 

 and carbonaceous and bituminous shale, and of mixed vegetable and 

 animal matters in the beds of bituminous limestone and calcareo- 

 bituminous shale. These conditions were those of the middle coal 

 formation. 



Within the limits of Nova Scotia, these conditions of deposition 

 applied, not to a wide and uninterrupted space, but to an area limited 

 and traversed by bands of Silurian and Devonian rocks, already 

 partially metamorphosed and elevated above the sea, and along the 

 margins of which igneous action still continued, as evidenced by the 

 beds of trap intercalated in the Lower Carboniferous ;* while about 

 the close of the Devonian period still more important injections and 

 intrusions of igneous matter had occurred, as shown by the granitic 

 dykes and masses which traverse the Devonian beds, but have not 

 penetrated the Carboniferous. -j- There is evidence, however, in the 



* Dawson, Quart. Journ. Geol. Soc, vol. i. p. 329. 

 t Dawson, Canadian Naturalist, 1860, p. 142. 



