356 PALEOZOIC TIME. 



were laid clown in a great estuary constituting the mouth of the St. 

 Lawrence, then the greatest river of the continent ; and this estuary 

 appears to have spread southward along the Bay of Fundy, and north- 

 ward and northeastward, over the St. Lawrence bay, to Newfound- 

 land ; for the coal-rocks cover even the extreme northern portion of 

 the peninsula of Nova Scotia. Hence the raised continental border 

 in this part probably lay as far out as eastern Newfoundland, from 

 which it may have stretched far enough southwestward to have shut 

 in also the Rhode Island region. The dip of the Nova Scotia Coal- 

 beds, and their great thickness at Pictou, on the shores of the Gulf, 

 show that only a small part of the originally great area is now above 

 the sea-level. 



Over these marshes, then, grew the clumsy Sigillarids and Catamites, 

 and the more graceful Tree-ferns, Lepidodendrids, and Conifers, with 

 an undergrowth of Ferns, and upon the dry slopes near by, forests of 

 Lepidodendrids, Conifers, and Tree-ferns ; and the luxuriant growth 

 was prolonged until the creeping centuries had piled up vegetable 

 debris enough for a coal-bed. Trees and shrubs were expanding, and 

 shedding their leaves and fruit, and dying, making the accumulation 

 of vegetable remains. Islands of vegetation, floating over the lakes, 

 may have contributed largely to the vegetable debris. Stumps stood 

 and decayed in the swamps, while the debris of the growing vegeta- 

 tion, or, in some cases, the detritus borne by the waters, accumulated 

 around them ; and their hollow interiors received sands, or leaves, or 

 bones, or became the haunts of reptiles, as was their chance. Logs 

 were floated off over the lakes, to sink and become buried in the 

 accumulating vegetable debris, or in deposits of detritus ; and some 

 of these transported stumps may have had aboard large stones, which 

 they finally dropped, and so put an occasional "bowlder" into the 

 forming beds. 



As already explained, there is no reason to suppose that the vege- 

 tation was confined to the lower lands : it probably spread over the 

 whole continent, to its most northern limits. It formed coal only 

 where there were marshes, and where the deposits of vegetable debris 

 afterward became covered by deposits of sand, clay, or other rock- 

 material. 



The condition of the continent just described represents only one 

 phase in the Carboniferous period. The rocks register a succession of 

 changes ; for coal-beds are succeeded by sandstones, or shales, or lime- 

 stones, or iron-ore beds, and many alternations of these beds, to a 

 thickness fifty times as great as that of the coal-beds. These inter- 

 vening strata, moreover, were sometimes of fresh- water origin ; and at 

 others, of marine : in the one case, containing fresh-water shells, or 



