ORIGIN OF COAL-FIELDS. 



[1653 



■\ve uttribute each coal-seam to a vegetation growing in swamps, 

 and not to the dri/tiiig of plants. It may be asked how during 

 )i\er imiiidatiijiid capable of sweeping ixwny thu leaves of fejus 

 and the stems and roots of Sigihariaa and other ti-ees, could the 

 waters fail to transport some fine mud into swamps? One gene- 

 ration iifter anotiier of tall trees grew with their roots in mud, 

 and they iiad fallen prostrate, had been turned into coal, were cov- 

 ei-ed with layers of nnid (now turned to shale), and yet the coal itself 

 has remained unsoiled during these various changes. The lecturer 

 thinks this enigma may be solved, by attending to what is now 

 taking place in deltas. The dense growth of reeds and herbage 

 which encompasses the margins of forest-covered swamps in the 

 valley and delta of the Mississippi, is such, that the fluviatile 

 waters in passing through them, are filtered and made clear to 

 themselves, entirely before they reach the areas which vegetable 

 matter may accumulate for centuries, forming coal if the climate 

 be f .^•orable. There is no possibilty of the least intermixture of 

 earthly matter in such cases. Thus in the large submerged tract 

 called the " Sunk Countr}'," near New Madrid, forming part of 

 the Western side of the valley of the Mississppi, erect trees have 

 been standing ever since the year 1811-12, killed by the great 

 earthquake of that date; Lacustrine and swamp plants have been 

 growing there in the shallows, and several rivers have inundated 

 the whole space, and yet have been unable to carry any sediment 

 ■within the outer boundaries of the morass. 



In the ancient coal of the South Joggins in Nova Scotia, many 

 of the underclays show a net work of Stigmaria roots, of which 

 some penetrate into or quite through older roots which belonged 

 to the trees of a preceding generation. Where trunks are seen 

 in an erect position buried in sandst ne and shale, rooted Sigil- 

 laria; or Cahunites, are often observed at diffei'ent heights in the 

 enveloyiing stratiV, attesting the growth of jilants at several suc- 

 sessive levels, wdiile the process of envelopment was going on. 

 In other cases there are jiroofs of the subtnergence of a forest 

 irader marine or brackish water, the base of the trunks of the 

 submerged trees being covered with serpuire or a species of spi- 

 rorljis. Not unfrequently seams of coal are succeeded by beds of 

 impure bituminous limestone, composed chiefly of compressed 

 Modiola3 with scales and teeth of fish, these being evidently depo- 

 sits of brackish or salt water origin. 



The leetuier exhibited a joint of the stem of a fresh water 

 veed ( Arundinaria muHcrospenna) covered with barnacles, 

 which he gathered at the extremity of the delta of the Mississip- 

 pi, or the Balize. He saw a cane-brake (as it is called in the 

 coimtry) of these tall reeds killed by salt water, and extending 

 over se\eral acr'cs, the sea having advanced over a space when the 

 discharge of fresh water had slackened for a season in one of the 

 vi\er's moutlis. Jf such reeds when dead could still remain 

 standing in the mud with b:irnacles attatched to them, (these 

 crustacese having been in tlieir turn destroyed by a return of the 

 river t ) the same spot,) still more easily may we conceive the 

 laro-e an 1 firndy rooted Sigillarire to have continued erect for 

 many vears in the Carboniferous Period, wlien the sea happened 

 to gain on any tract of submerged land. 



Submorgpuco under salt water may have been caused eitlier 

 by a local diminution in the discharge of a river in one of its many 

 mouths, or more probably by subsidence, as in the case f the 

 erect coluums of the Temple of Sorapis. near Naples, to which 

 Serpula; and other marine bodies arc "^till found adhering. 



Sir Charles next entered into some speculations respecting the 

 probaVjle volume of soliil matter contained in the carboi.ifcrous 

 formation of Nova Scotia. The data lie raid for such an esti- 

 mate are as yet imperfect, Ijut some advantages would be gained 

 could we but make some slight approximation to the truth. The 



strata at the South Joggins are nearly three miles thick, and they 

 are known to be also of enormous thickness in the district of the 

 the Albion Mines near Pictuu, more than one hundred miles to 

 the eastward. There ai>|>ears therefore little danger of erring on 

 the side of excess, if we tfike half that amount or 75UO feet as 

 the average thickness of the whole of the coal measures. The 

 area of the coal-tiekl, including part of New Biunswick, to the 

 we.-t, and Prince Edward's Island and the Magdalen Isks to the 

 north, as well as the Cape Breton beds together with tlie connecting 

 strata which must have been denuded or must still be concealed be- 

 neath the waters of the Gulf of St. Lawrence, may comprise 

 about 36,000 square miles, which with the thickness of VoOO 

 feet before assumed will give 7,527,108,000,000,000 cubic feet, 

 (or 51, 136. 4 cubic miles) of solid matter as the volume of the 

 rocks. Such an array of figures convey no distinct idea to the 

 mind ; but is interesting when we reflect that the Mississippi 

 would take more than two million of years (2,033,000) to 

 convey to the Gulf of Mexico, an equal quantity of solid matter 

 in the shape of sediment, assuming t e average discharge of wa- 

 tei', in the great rivei', to be as calculated by Mr. Forshey, 450,- 

 000 cubic feet per second, throughout the year, and the total 

 quantity of mud to be as estimated by Mr. Riddell, 3,702,758,- 

 400 cubic feet in the year.* 



We may, however, if we desire to reduce to a minimum the 

 possible time required for such an operation, (assuming it to be 

 one of tluviatile denudation and deposition,) select as our agent, 

 a river flowing from a tropical country, such as the Ganges, in 

 the basin of which the fall of rain is much heavier, and where 

 nearly all comes down in a third part of the year, so that the 

 river is more turbid than if it flowed in temperate latitudes. In 

 reference to the Ganges, also, it may be well to mention, that its 

 delta presents in one respect a striking parallel to the Nova 

 Scotia Coalfield, since at Calcutta the depth, of eight or ten 

 feet from the suiface, bnried trees and roots have been found in 

 digging tanks, indicating an ancient soil now underground; and 

 in boring on the same site for an Artesian well to the depth of 

 481 feet, other signs of ancient forest-covered lands and peaty 

 soils have been observed at several dej.ths, even as far down as 

 300 feet and more below the level of the sea. As the strata 

 pierced through contained fresh water remains of recent species 

 of plants and animals, they imply a subsidence, which has been 

 going on contemporaneously with tlio accumulation of fluviatile 

 mud. 



Captain Strachey of the Bengal Engineers has estimated that 

 the Ganges must discharge 4^ times as much water into the Bay 

 of Bengal, as the same river carries past Ghazipore, a place 500 

 miles above its mouth, wdiere ex])eriments were made on the 

 volume of water and pioportion of mud by the Rev. Mr. Everest. 

 It is not till after it has ])asseil Ghazipore, that the great river is 

 joined by most of its larger tiibutan'es. Taking the qnantit)' of 

 sediment at one-third less than that assigned by Mr. Evt-rest for 

 the Ghazipore average, the volume of solid matter conveyed to 

 the Bay of Bengal would still amount to 20,000 millions of 

 cubic feet annually. The Ganges therefore might accomplish in 

 three hundred and senventy-five thousand years the. task wdiich 

 it would take the Mississi]ipi, according to the data before laid 

 down, upwards of two million years to achieve. 



One inducement to call attenion to such calculations is the 

 hope of interesting engineers in making accurate measurement of 

 the ([uantity of water and nnid discharged by such rivers as 

 the Ganges, Brahmapootra, Indus?, and Mississippi, and to lead 

 geologists to ascertain the number of cubic feet of solid matter, 

 which ancient fluviatile formations, such as the coal-measures, 



•Sec Principles of Geology, 8th ed., p. 19. 



