354 G. W. Bulman — On Under clay a. 



FEET 



(2). Brown silt ... ... ... ... 3 



Black peat ... ... ... ... OJ 



Sandy silt and loam -with marine shells ... 5 



Yellowish clay ... ... ... ... 2 



Grey peaty clay ... ... ... ... 3 



Soft, clean, bhie clay ... ... ... 2 



Peaty layer with drift wood and hazel nuts ... 0| 

 Gravelly clay (? Boulder-clay) touched 



(Pit two furlongs East of Doveham. p. 108.) 



(3). Peat ... ... ... ... ... 1 



Clay with Marine shells ... ... ... 6 



Silt, sandy ... ... ... ... 3 



Peat with trees ... ... ... ... 1\ 



Gravel... ... ... ... ... 10? 



(Tattershall Brickyard at Dogdyke near mouth of River Bain. p. 111.) 



The view advocated in the above memoir is that these deposits 

 are the result of the silting up of a bay, and that they are marine 

 deposits. The layers of peat occurring at various levels are held to 

 be indications of old land surfaces. If this is so we must suppose 

 there has been a filling up of the bay followed by a depression after 

 its growth, for each bed of peat. Of such earth movements in the 

 area under consideration there appears to be no independent proof, 

 or we should have here a valuable illustration of the modern view 

 of the origin of coal in situ with slow and intermittent subsidence. 

 But some of the sections indicate rather a drift origin for some of 

 the lower layers of peat. Thus in section (1) the peat rests on 

 coarse angular savcl, and in (3) on gravel, neither of which seems 

 a likely substratum for a peat moss to flourish on. In (2), again, 

 the layer of peat itself contains "drift wood" which is strongly 

 suggestive of a drift origin for the peat itself. 



The clay beneath the peat also frequently contains marine shells, 

 which have apparently never been found in the underclays of the 

 Carboniferous. On the whole, then, it does not seem that the beds 

 commonly found beneath layers of peat throw much light on the 

 origin of Carboniferous underclays. Yet the occurrence of snch 

 fine-grained deposits as these clays, as the final member of the 

 series in the silting up of an area, and just before the growth of 

 vegetation, is a valuable suggestion as to how an underclay might, 

 under certain conditions, be formed in a shallowing area, and in 

 immediate proximity to land. 



The conditions in the Fen district ai'e, however, somewhat peculiar, 

 for the clays are marine deposits, and must have been brought by 

 currents from considerable distances. 



It has been asserted that Stigmaria are of universal occurrence in 

 underclays. Thus Professor Green writes of them, "They always 

 contain a peculiar vegetable fossil known as Stigmaria " (Physical 

 Geology, p. 258). 



And this — on the hypothesis that Stigmaria are the roots of the 

 vegetation which forms the coal — is one of the strongest arguments 

 that the underclays are old soils. But it is to be observed that 

 while Stigmaria appear to be of almost — if not quite — universal 

 occurrence in underclays, they are also often found in sandstones, 



