CONDITIONS OF DEPOSITION OF THE BEDS. 133 



Carboniferous rocks of the Magdalen Islands and of Newfoundland, 

 and in the fringes of such rocks on parts of the coast of Nova Scotia • 

 and New England, that the area in question was only a part of a far 

 more extensive region of Carboniferous deposition, the greater part 

 of which is still under the waters of the Atlantic and of the Gulf of 

 St Lawrence. 



There is ample proof that most of the coarser matter of the Car- 

 boniferous rocks was derived from the neighbouring metamorphic 

 ridges ; but much of the finer material was probably drifted from more 

 distant sources. There seems no good reason to doubt that in the 

 Carboniferous period, and especially in those portions of it in which 

 the areas now under consideration were in the condition of shallow 

 seas or swampy flats, the greater part of the Laurentian and Sil- 

 urian districts of North America existed as land; while the great 

 number of coal formation plants common to Europe and America may 

 indicate the existence of intermediate lands now submerged. From 

 such lands, undergoing waste during the long Carboniferous period, 

 the materials of the shales and finer sandstones may have been derived. 



Taking this view of the source of the sediment, we should infer 

 that the time of the formation of the marine limestones was that of 

 greatest depression of the land, when the local ridges of older rock 

 were mere reefs and islets, and when sediment from more distant 

 lands was deposited only at intervals. We should also infer that the 

 time of the formation of the coal-beds was that of greatest elevation, 

 when the former sea-bottoms had become land-surfaces or flats, 

 exposed only to occasional inundation, and when rivers were bearing 

 downward from large continental regions great quantities of fine silt. 

 Farther, the conditions of the millstone-grit and of the newer coal 

 formation must have been of an intermediate character, requiring wide 

 sea areas receiving great quantities of sediment ; and on this account, 

 as well as because of their shallowness, unfavourable to marine life, 

 while the areas of vegetable growth were also of limited extent. 



It would also follow that when the lower coal measures and 

 conglomerates were formed, the land was slowly subsiding; that in 

 the time of the marine limestones it attained to its greatest depression, 

 and long remained nearly stationary ; that in the Millstone-grit period 

 there w r as re-elevation, and that in the period of the middle coal 

 formation and Newer Coal formation there was again subsidence, slow 

 and interrupted at first, but subsequently of greater amount. From 

 the absence of Permian deposits, it may be inferred that elevation 

 again took place at the close of the Carboniferous period, to such an 



* Jukes's " Newfoundland : " infra, chap. xiii. 



