part 4] THE MILLSTONE GRIT OF YORKSHIRE. 277 



in Millstone Grit times. The area covered in Yorkshire by this 

 series at present is no less than 840 square miles ; while if we take 

 into account that which lies beneath the newer rocks, and that 

 where it can be safely assumed to have occurred (but is now only 

 represented by outliers on such hills of the Pennine Chain as 

 Ingleborough, Whernside, Penygent, etc.), an area of 2000 square 

 miles once occupied by Millstone Grit would be a safe assumption. 

 If we take 1000 feet as the average thickness, this would represent 

 400 cubic miles ; or it may be built into the form of a range of 

 hills, which would be 800 miles long, 1 mile in diameter at the 

 base, and 1 mile high. 



Now, since it is an axiom in geology that deposition is a measure 

 of detrition, we may form some idea of the vast amount of 

 material which was removed from some pre-existing land-surface. 

 This is all the more evident when it is remembered that in such 

 an estimate as that given above, only Yorkshire has been considered, 

 and the amount would have to be multiplied by a large factor 

 were the Millstone Grit of other areas in the Midlands and North 

 of England, etc., to be taken into account. 



IX. Position of the Ancient Land-Mass. 



If we take first the position, the discussion will gain in clearness 

 if a survey is taken of the Millstone Grit as it occurs in Lanca- 

 shire and Yorkshire, and to the south in Staffordshire, Derbyshire, 

 Cheshire, and Leieestershire. In papers by E. Hull and A. H. 

 Green 1 describing the Millstone Grit of these areas, it is shown 

 very clearly that there is a very pronounced attenuation of the series 

 where traced towards the south and south-east. In the summary 

 given at the end of the first paper mentioned, it is stated: — 



' We have now traced the Millstone Grit from the borders of Lancashire 

 and Yorkshire, where it contains five thick beds of massive gritstone and 

 reaches a thickness of 2800 feet, to the borders of the North Staffordshire 

 Coalfield, where only two of these beds are left, and where the whole thick- 

 ness is not more than 200-300 feet. We find the Rough Rock present 



everywhere and keeping pretty much the same thickness throughout, but 

 losing altogether its coarseness and massive character in the south. The 

 Haslingden Flags, the second bed, maintain their thickness and character 

 unchanged until they thin away somewhat suddenly about 5 miles south-west 

 of Buxton. The Third Grit runs through the whole of the district ; but, from 

 a, thickness of more than 400 feet, which it reaches in Lancashire, it lessens 

 down to about 100 feet in the neighbourhood of Congleton, and still further 

 south seems to be on the point of dying out altogether. Though this bed 

 becomes without doubt finer to the south, it keeps more than any other a 



certain massiveness of structure to the last The passage of the fourth 



or Kinderscout rock from an enormous mass of gritstone and conglomerate 

 1000 feet thick into two beds of finer gritstone with a shale between, 

 north of Buxton, has been pointed out. as also the further change which the 

 latter undergo into still finer sandstones, and their total disappearance in the 

 Biddulph and Rudyerd basins.' 



The sections which are given to illustrate this attenuation are 

 here reproduced (see fig. 1, p. 278). 



1 Q.J.G.S.vol. xx (1864) pp. 242-67 ; alsoi&td. vol. xxiv (1868) pp. .°»19-23. 

 Q. J. G. S. No. 300. v 



