Ch. XXIV.] LONG PERIODS OF ACCUMULATION. 383 



trees and semi-aquatic plants. As a singular proof of this fact, I may 

 mention that whenever any part of a swamp in Louisiana is dried up, 

 during an unusually hot season, and the wood set on fire, pits are 

 burnt into the ground many feet deep, or as far down as the fire can 

 descend, without meeting with water, and it is then found that scarcely 

 any residuum or earthy matter is left.* At the bottom of all these 

 " cypress swamps" a bed of clay is found, with roots of the tall cypress 

 (Taxodium distickum), just as the underclays of the coal are filled with 

 Stigrnaria. 



It has been already stated, that the carboniferous strata at the South 

 Joggins, in Nova Scotia, are nearly three miles thick, and £he coal- 

 measures are ascertained to be of vast thickness near Pictou, more than 

 100 miles to the eastward. If, therefore, we speculate on the probable 

 volume of solid matter, contained in the Nova Scotia coal-fields, there 

 appears little danger of erring on the side of excess if we take the 

 average thickness of the beds at 7500 feet, or about half that ascertained 

 to exist in one carefully-measured section. As to the area of the coal- 

 field, it includes a large part of New Brunswick to the west, and extends 

 north to Prince Edward's Island, and probably to the Magdalen Isles. 

 When we add the Cape Breton beds, and the connecting strata, which 

 must have been denuded or are still concealed beneath the waters of the 

 Gulf of St. Lawrence, we obtain an area comprising about 36,000 square 

 miles. This, with the thickness of 7500 feet before assumed, will give 

 51,000 cubic miles of solid matter as the volume of the carboniferous 

 rocks. 



The Mississippi would take more than two million of years to convey 

 to the Gulf of Mexico an equal quantity of solid matter in the shape 

 of sediment, assuming the average discharge of water, in that great river 

 to ba as calculated by Mr. Forshey, 450,000 cubic feet per second, 

 througnout the year, and the total quantity of mud to be, as estimated by 

 Mr. Riddell, 3,702,758,400 cubic feet in the year.f 



The Ganges, according to the data supplied to me by Mr. Everest and 

 Captain Strachey, conveys so much larger a volume of solid matter an- 

 nually to the Bay of Bengal, that it might accomplish a similar task in 

 375,000 years, or in less than a fifth of the time which the Mississippi 

 would require.^ 



As the lowest of the carboniferous strata of Nova Scotia, like the 

 middle and uppermost, consist of shallow-water beds, the whole vertical 

 subsidence of three miles, at the South Joggins, must have taken place 

 gradually. If then this depression was brought about in the course of 

 375,000 years, it did not exceed the rate of four feet in a century, resem- 

 bling that now experienced in certain countries, where, whether the 



* Lyell's Second Visit to the U. S., vol. ii. p. 245 ; and American Journ. of 

 Science, 2d series, vol. v. p. 17. 



f Principles of Geology, 9th ed. 1853, p. 273. 

 % Ibid. 1853, p. 283. 



