140 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



great indeed. The three divisions of the Coal-measures attain a 

 thickness of 6000 feet, in addition to which the Millstone- grit and 

 Yoredale series are about 4000 feet, forming in all 10,000 feet of 

 sedimentary strata, which is an increase of 6550 feet over the War- 

 wickshire coal-field. The Carboniferous sands and clays appear to 

 have been poured in greatest quantity along a tract of country 

 running south-eastward through this district, causing the isometric 

 lines to make a southerly bend when crossing it, and entitle this 

 tract to be called "■ the line of maximum accumulation " *. 



Flintshire and Derbyshire. — The development of both the calca- 

 reous and " sedimentary " elements in these counties are probably 

 nearly similar. The combined thickness of the upper, middle, and 

 lower Coal-measures reaches 3000 feet ; and the Millstone-grit series 

 from 800 to 1000 ; in aU 3800 or 4000 feet. The Carboniferous Lime- 

 stone varies from 1000 to 1500 feet f. 



Anglesea. — The thickness of the Carboniferous series in Anglesea 

 (as determined by Prof. Eamsay) is as follows : — Coal-measures, 

 1300 feet ; Millstone-grit, 200 feet ; Carboniferous Limestone (con- 

 taining some beds of sandstone and shale), 450 feet X '- separating 

 the two elements we may say for the " sedimentary," 1600 feet ; 

 for the calcareous, 360 feet. The whole series, however, is not pre- 

 sent, as the little coal-field has suffered from denudation, for which 

 allowance must be made. 



Notts, Derbyshire, and Yorkshire. — Crossing the limestone anti- 

 clinal into Derbyshire, we find the thickness of the strata in the neigh- 

 bourhood of Alfreton as follows : — lower (or Gannister series), middle 

 and upper measures, 3500 feet; Millstone- grit and Yoredale series, 

 600 feet ; in aU 4100 feet. As we do not, however, throughout the 

 whole of this great coal-field reach the top of the Carboniferous 

 rocks, which have either been denuded or are hidden beneath the 

 Magnesian Limestone, several hundred feet ought to be added to 

 the above, making the total thickness about 4500 feet, as compared 

 with 2600 feet in Leicestershire. The thickness of these strata 

 augments, though not rapidly, along their extension into Yorkshire. 

 The development of the series in Durham varies from 3500 to 4000 

 feet. 



Lancashire. — In this county there is a greater development of 

 Carboniferous sedimentary strata than in any district in England. 

 The upper Coal-series of Manchester is 2000 feet in thickness ; the 

 middle, 3200 feet ; and the lower, 2000 feet ; the thickness of the 

 Millstone-grit series is unascertained, but is at least 3000 feet ; and 

 the Yoredale Rocks, 2000 feet ; in aU 12,200 feet. This thickness is 



* I may here explain that it appears probable that the barrier of land was 

 broken through to the south of Warwickshire, allowing the northern current, 

 which brought the sediment, to escape through the opening. (See Map.) On this 

 hypothesis we can explain the enormous accumulation of sediment along this 

 line. The thicknesses of the strata are taken from several sections made by the 

 Geological Survey. 



t These tliicknesses are taken from the horizontal section by the Geological 

 Survey. 



I Horizontal Sections, Sheet 40, with description. 



