138 THE CARBONIFEROUS SYSTEM. 



divide geological time into determinate natural cycles, the parts of 

 which are analogous to those of similar cycles. A further question 

 to be solved is, whether such cycles corresponded in all parts of the 

 world, or whether, as is more likely, the earth might be divided into 

 areas in which in each cycle elevation and subsidence were contem- 

 poraneous. So far as the present subject is concerned, I merely desire 

 to show that the Carboniferous rocks of Nova Scotia represent a 

 complete cycle of the earth's history, and correspond in time with the 

 Carboniferous of Europe, and in value with the other great divisions 

 of the Palaeozoic age. 



Summary of facts relating to the mode of accumulation of Coal. 



With regard to this important subject, I would rather invite 

 attention to the details to be presented in subsequent pages, than 

 make any preliminary general statements. It is, however, necessary 

 to notice here the several views which have prevailed as to the probable 

 accumulation of coal by driftage or growth in situ, in water or on laud. 

 I liave already, in previous publications,* stated very fully the 

 conclusions at which I have arrived on some portions of this subject, 

 and I would now sum up the more important general truths as 

 follows : — (1.) The occurrence of Stigmaria under nearly every bed of 

 coal, proves beyond question that the material was accumulated by 

 growth in situ; while the character of the sediments intervening 

 between the beds of coal proves with equal certainty the abundant 

 transport of mud and sand by water. In other words, conditions 

 similar to those of the swampy deltas of great rivers are implied. (2.) 

 The true coal consists principally of the flattened bark of Sigillarioid 

 and other trees, intermixed with leaves of ferns and Cordaites, and 

 other herbaceous debris, and with fragments of decayed wood consti- 

 tuting " mineral charcoal," all these materials having manifestly alike 

 grown and accumulated where we find them. (3.) The microscopical 

 structure and chemical composition of the beds of cannel-coal and 

 eartliy bitumen, and of the more highly bituminous and carbonaceous 

 shales, show them to have been of the nature of the fine vegetable 

 mud which accumulates in the ponds and shallow lakes of modern 

 swamps. When such fine vegetable sediment is mixed, as is often 

 the case, with clay, it becomes similar to the bituminous limestone 

 and calcareo-bituminous shales of the coal measures. (4.) A few of 

 the underclays which support beds of coal are of the nature of the 

 vegetable mud above referred to ; but the greater part are argillo- 



* "On the Structures of Coal," Quart. Journ. Geol. See., vol. xv., also vol. xxii., 

 p. 95, etc. " Air-breathers of the Coal Period," Montreal, 1863, p. 18. 



