THE GROWTH OF COAL 239 



his observations, examining in detail every one of eighty-one 

 Coal Groups, as I have called them, each consisting of at 

 least one bed of coal, large or small, with its accompaniments, 

 and in many cases of several small seams with intervening 

 clays or shales. * In nearly every case the Stigmaria " under- 

 clay " is distinctly recognisable, and often in a single coal 

 group there are several small seams separated by underclays 

 with roots and rootlets. These underclays are veritable fossil 

 soils ; sometimes bleached clays or sands, like the subsoils of 

 modern swamps ; sometimes loamy or sandy, or of the nature 

 of hardened vegetable mould. They rarely contain any remains 

 of aquatic animals, or of animals of any kind, but are filled 

 with stigmaria roots and rootlets, and sometimes hold a few 

 prostrate stems of trees. 2 While the underclay is thus a fossil 

 soil, the roof or bed above the coal, usually of a shaly char- 

 acter, is full of remains of leaves and stems and fruits, and 

 often holds erect stumps, the remains of the last trees that 

 grew in the swamp before it was finally covered up. 



Some of the thinnest coals, and some beds so thin and 

 impure that they can scarcely be called coals at all, are the 

 most instructive. Witness the following from my section of 

 the South Joggins. 



Coal Group i, of Division 3, is the highest of the series. Its 

 section is as follows : 



" Grey argillaceous shale. 

 Coal, i inch. 

 Grey argillaceous underclay, Stigmaria. 



"The roof holds abundance of fern leaves (Alethopteris 



1 For details see Journal Geol. Society of London, 1865 ; and " Acadian 

 Geology," last edition, 1891. 



2 At the South Joggins, in two or three cases, beds of bituminous shale 

 full of Naiadites and Cyprids have by elevation and drying become fit 

 for the growth of trees with stigmaria roots ; but this is quite exceptional, 

 no doubt arising from the accidental draining of lakes or lagoons on their 

 elevation above the sea level. 



