356 G. W. Bulman — On Underdaijs. 



Of these lie remarks : "In no instance could I detect avy trmik 

 intersecting a layer of coal, however thin ; and most of the trees 

 terminated downwards in seams of coal " (Elements of Geology, 

 p. 391). 



Yet had the nnderclay been really the ancient soil we might 

 reasonably expect to find the trees extending downwards to it. 



This south Joggins section is described in more detail by Sir 

 J. W. Dawson (Acadian Geology, chap. xl.). In glancing through 

 the details of the beds there given it is observable that the greater 

 riumher of erect trees are in the roofs of the Coal-seams. The erect 

 position of such trees is generally supposed to indicate that they 

 are in their original position of growth. M. Fayol, however, has 

 pointed out that in the Coal-fields of Central France a certain 

 number of stumps of trees occur at right angles to the planes of 

 bedding, although a larger number are horizontal, or inclined at 

 various angles ; and yet he has, I think, conclusively shown that 

 the coal of this district is of drift origin. Hence we must admit 

 that the occurrence of a few erect trees is in itself no sufficient 

 evidence that they are in the position of growth. 



Dr. Croll has pointed out the almost entire absence of old land 

 surfaces throughout the geological series except the coal and under- 

 clays of the Carboniferous. The familiar " Dirt bed " of the Isle of 

 Portland is one of the few exceptions. We must also except the 

 Coal seams of the Yorkshire Oolite of which Sir A. Ramsay has said 

 that they " have not been formed of drift vegetation, for underneath 

 each bed there occurs an underclay, or old soil, charged with the 

 roots of those plants the decay of which on the spot formed the thin 

 beds of coal" (Physical Geology of Great Britain, pp. 194-5). 



And Sir J. W. Dawson writing of the strata of the Brian 

 (=: Devonian) system of America, states that they " include fossil 

 soils of the nature of underclays, in which little else appears to have 

 grown than a dense herbage of Psilophijton, along with plants of the 

 genus Arthrostigma " (Geological History of Plants, p. 105). 



If, then, we accept the belief that the underclays of the Carbon- 

 iferous are old land surfaces we are foi'ced to the conclusion that the 

 physical conditions of that period have been unique — at least as far 

 as regards Europe. Perhaps, however, this conclusion is inevitable 

 in whatever light we regard the underclays. 



Sir Wm. Logan considered it a universal rule in the South Wales 

 Coal-field that a bed of coal reposed on an underclay, and the 

 generalisation has been extended to all our Coal-fields. But there 

 are exceptions, and coal is found at times resting on ordinary 

 sandstone or shale. And underclays without any Coal-seams resting 

 upon them are of common occurrence. Thus in the South Joggins 

 section of 14,570 feet in thickness there are said to be 76 coal seams 

 and 90 stigmarian underclays ; so that at least 14 of these latter are 

 without accompanying coal. Indeed, according to Sir J. W. 

 Dawson's method of interpretation there are something like 2138 old 

 land surfaces in this remarkable section, and he notes that " the 

 forest soils are much more frequently preserved than the forests 

 themselves " (Acadian Geology, p. 186). 



