LYELL'S TRAVELS IN NORTH AMERICA. 397 



the general rule. There must, for example, be an absence of waves and currents 

 of sufficient strength to loosen and overturn the trees, and the water must be 

 charged with sediment ready to envelope the plants before they have had time 

 totally to decay. I have shown that on the coast of S. Carolina and Georgia 

 the land sunk in modern times, and that buried trees are occasionally found in 

 strata containing shells of recent species. The formation of low islands of sand 

 off the shore, breaking the force of the Atlantic, has probably allowed many of 

 these trees near the mouths of estuaries to continue erect under water, until they 

 were silted up and preserved, Similar low islands and sandbanks skirt nearly 

 the whole of the eastern coast of the United States, and may assist the geologist 

 in explaining some of the phenomena of the Carboniferous period, especially 

 the manner in which superficial beds of vegetable matter, as well as upright 

 trees, escaped the denuding forces. 



Thirdly. It has been objected to the theory which refers the origin of seams 

 of pure coal to plants which grew on the exact spaces where we now find coal, 

 that the surfaces of ancient continents and islands ought to undulate like those 

 we now inhabit. Where, they ask, are the signs of hills and valleys, and those 

 river-channels which cut through deltas? These apparent difficulties will, I 

 think, be removed, if we reflect that the fossilisation of successive forests pre- 

 supposes both the subsidence of the ground and the deposition of sediment going 

 on simultaneously. If so, the accumulation of mud and sand furnishes us with 

 the levelling power required, and, had there been extensive denudation capable 

 of producing valleys, it could readily have swept away all the coal. In regard 

 to ancient river-courses, the late Mr. Buddie often assured me, that he had in 

 many places met with them in the coal-fields of the North of England, and he 

 has given a detailed account of one which intersected a seam of coal in the 

 Forest of Dean, Even in these cases, however, the general evenness of the 

 surface is immediately restored by a new sinking of the delta, and the depo- 

 sition of fresh sediment, so that the succeeding seam of coal has grown on as 

 perfectly flat a surface as if there had been no partial destruction of the beds 

 below. 



If it be objected that, according to the analogy of recent subterranean move- 

 ments, some areas ought to have sunk down at a more rapid rate than others, 

 producing irregularities in the ancient level of the dry land, we reply, that 

 there are abundant proofs in the arrangement of the carboniferous strata, that 

 the amount of local subsidence was actually not uniform. Mr. Bowman has 

 clearly pointed out, that the wedge-shaped or lenticular masses of sandstone and 

 shale, which sometimes intervene between the upper and lower portions of a 

 seam of coal, are the natural result of such inequalities in the downward move- 

 ment. In those areas which sink so fast as to be submerged, the growth of 

 terrestrial plants is suddenly arrested, and the depressed region becomes the 

 receptacle of sediment, until its level is again raised. Then the growth of the 

 former vegetation is resumed, and the result is, the intercalation of strata for a 

 certain space between two beds of coal, which unite and become one, if they are 

 followed to a certain distance in every direction. Vol. ii. pp. 179 — 193. 



The continent of America is well known to exhibit but very few 

 indications of rocks of the secondary period, or at any rate of the 

 triassic and oolitic series. Still the lower beds are by no means 

 wanting, and the red sandstone of Connecticut, although it has 

 been referred by some geologists to the Permian system, and is, 

 perhaps, to a certain extent, a passage bed, appears to be, on the 

 whole, more properly referred to the trias, and must, at least for 

 the present, be looked upon as of that age. This rock has long been 

 celebrated for the impressions of footsteps of birds with which its 

 slabs are in many places covered, and Mr. Lyell mentions that since 

 these impressions were first announced by Professor Hitchcock in 



