1865.] DAWSON COAL-FOKMATION. 108 



Of course such parallelism might be variously expressed by reckon- 

 ing a smaller or larger number of groups. Independently of these 

 different modes of statement, however, I believe that the basis -of 

 such comparisons exists in nature, and that it will prove possible to 

 subdivide 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 CaHoniferous of Europe, and in value with the other great 

 divisions of the Palaeozoic age. 



4. Summary of facts relating to the m^ode of accumulation of Goal. 

 - — ^With regard to the more special subject of this paper, I would 

 rather invite attention to the details to be presented under the next 

 head, than make any preliminary general statements. It is, how- 

 ever, 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 land. I have 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 import- 

 ant 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 m 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 constituting " 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 earthy bitumen, and of 

 the more highly bituminous and carbonaceous shales, show them to 

 have been of the nature of the fine vegetable mud which accumu- 

 lates in the ponds and shallow lakes of modern swamps. When 

 such fine vegetable sediment is mixed, as is often the case, with 

 shales, it becomes similar to the bituminous limestone and calcareo- 

 bituminous shales of the Coal-measures. (4) A few of the under- 

 clays which support beds of coal are of the nature of the vegetable 

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

 in composition, with little vegetable matter, and bleached by the 

 drainage from them of water containing the products of vegetable 

 decay. They are, in short, loamy or clay soils, and must have been 

 sufficiently above water to admit of drainage. The absence of sul- 



* " On the Structures of Coal," Quart. Journ. Geol. See, vol. xv. Air-breathers 

 of the Coal Period, Montreal, 1863, p. 18. 



I 2 



