Reviews— Geology of South Wales Coalfield. 135 



VIII. — Origin of Coal. 

 By J. E. Dakyns, Esq. 



IN his interesting paper on " The Origin of Coal," published in 

 the Geological Magazine for January, 1901, p. 29, Mr. Strahan 

 says : " the Limestone Series generally consists of repetitions of small 

 groups of strata, each group being composed of sandstone, followed 

 by shale, shale followed by limestone." It is not stated whether 

 this is intended to be an upward or downward succession ; but 

 if the former is meant, as it seems to be, the sequence is very 

 different from that which exists in many parts of the country. 

 Amongst the Yoredale Kocks proper — by which I mean the beds 

 in the valley of the Yore and in such parts of the neighbourhood 

 as contain rocks of a similar type — the usual upward succession 

 is sandstone followed by limestone overlaid by shale. That is to 

 say, the limestones very often have basement sandstones, and are 

 nearly always immediately overlaid by shale. There are some 

 cases in which limestone is overlaid by sandstone, but these are 

 quite exceptional. 



As it seems from recent discussions at Bradford to be not generally 

 known, I may as well state that the Yoredale type of beds does not 

 exist south of the Craven fault ; as a matter of fact, it dies out 

 between Kettlewell and Grassington. 



Mr. Strahan also says that " underclays do not resemble soils, 

 inasmuch as they are perfectly homogeneous." Now on many parts 

 of the Millstone Grit moorlands in Yorkshire, the hill peat rests 

 on yellowish clay, formed by the decomposition of the underlying 

 rocks. This clay (which may be called the peat underclay) looks 

 BO like a Coal-measure underclay, that one is led to think that both 

 had a similar origin, however different may have been the circum- 

 stances. Of course, when an underclay occurs in the midst of a coal, 

 or on top of coal, it cannot have been formed by decomposition of 

 underlying rock. In such cases, which are exceptional, it must have 

 been drifted somewhat. But even if all underclays were drifted, 

 that would not prevent their having been the seats on which coal- 

 forming plants grew, and the striking resemblance of peat underclays 

 to coal underclays makes me think that the latter clays were the 

 seats on which the coal plants grew. 



IS, IE V I E ^W S. 



I.— Geology of the South Wales Coalfield. Part II : 



The Country around Abergavenny. By Aubrey Strahan, 



M.A., F.G.S., and Walcot Gibson, F.G.S. ; with Notes by J. K. 



Pakyns, M.A., and Prof. W. W. Watts, M.A., F.G.S. Memoirs 



of the Geological Survey. 8vo ; pp. 103. (London : printed for 



H.M. Stationery Office, 1900. Price 2s.) 



rnmS memoir is written in explanation of the New Series map 



JL sheet 232. It includes a brief account of the Silurian rocks 



of part of the Usk iulier, and a fuller account of the Old Bed 



