138 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. [Feb. 5, 



From this old land, however, little or no sediment was given oif, as 

 the limestone attains a very great thickness, and is pure dolomite at 

 a short distance from the present site of the Cambrian rocks *. Over 

 Derbyshire the sea must have been remarkably clear; but it became 

 more muddy northward, till in Scotland the sediment was so abun- 

 dant as to extinguish life in the Crinoids and Corals, by whose 

 labours the limestone was formed. Hence we have a clear ^roof that 

 the sources of the sediment were in the north. 



In Yorkshire these variations in the relative distribution of the 

 calcareous and non- calcareous strata of this group have long since 

 been pointed out by Prof. Phillips. In a diagram appended to ' The 

 Geology of Yorkshire ' these variations are represented by an in- 

 genious design, " and prove," as the author remarks, " that the 

 agencies which resulted in the formation of the limestone acted with 

 greatest effect from the south-east, while those which resulted in 

 the deposition of sandstones and shales acted with greatest effect 

 from the north-west." 



He then proceeds to trace the range of the Lower Sear-limestone, 

 showing that towards the south-east of its course between Ribbles- 

 dale and Wharfdale it is 1000 feet in thickness. Northward at 

 Pen-y-ghent it is about 600 feet; at Kirkby Stephen even less. North 

 of the line from Kettlewell to Bar Fell it becomes split up by beds of 

 shale, grit, and coal, which continually augment northwards, until at 

 length it assumes all the characters of the Lower Carboniferous 

 group of Scotland. 



He then shows that the Yoredale series increases in thickness 

 towards the north-west (that is, in the direction along which the 

 limestone becomes attenuated), attaining at Bar Fell 1000 feet or 

 more, and dwindling down to 300 feet under Great Whernside. 



These passages describe changes in the Lower Carboniferous series 

 of Yorkshire, which are applicable on a much wider stage to Eng- 

 land and Scotland, from the edge of the harrier northwards. Had 

 Prof. Phillips extended his observations, and foUowed out the train 

 of thought upon which he had entered, I can well understand what a 

 fund of illustration and force of reasoning this subject would have 

 received at his hands. 



The thickness of the Carboniferous Limestone over every part of 

 Britain is indicated by the isometric lines on the Map. These thick- 

 nesses have been obtained from the carefully measured sections of 

 the Geological Survey — so far as it has extended, — and from the 

 published works of various authors on the northern districts of Eng- 

 land and in Scotland: the following are a few special instances. 

 Thus, the thickness of the limestone in Coalbrook-Dale is 50 to 100 

 feet ; in Denbighshire, 1000 to 1500 feet ; in Flintshire, 1000 to 

 1500 feet ; Anglesea, 360 feet ; south side of the Lake District, 

 1500 feet; Scottish Borders, 500 feet; the Lothians, 162^feet; and 

 Lanarkshire, less. In Fifeshire it is sometimes on the point of ex- 

 piring. 



* At Breedon Cloud, where its thicfcaess is upwards of 1000 feet, vfith few or 

 no bands of shale. 



