1862.] hull caebonifeeotjs strata. 137 



1 . Eegion North of the Barrier. 



(a.) South-easterly attenuation of the " Sedimentary^' Strata; 

 North-westerly attenuation of the Calcareous Strata. — If we take a 

 series of vertical sections of the various sandstones, grits, and shales 

 of the Carboniferous Period, from the midland counties of Lei- 

 cester, Warwick, and South Stafford, then through the adjoining 

 districts to the north, and ultimately into Scotland, we shall 

 find a constant accession of material along this course. Thus, I 

 find that the increase from Leicestershire to Lancashire, along a 

 line running north-west, is no less than 8000 feet of strata in a 

 horizontal distance of 65 miles, which gives a slope of 1 in 43, or 

 about 1° 30', as the angle of increment of sediment in this distance ; 

 the maximum thickness of the strata in Lancashire being 12,000 

 feet, and in Leicestershire 4000 feet. 



If, on the other hand, we make a similar series of sections of the 

 limestones, from Derbyshire as a centre, either west, north-west, 

 or north, we shall find that these calcareous strata constantly di- 

 minish in thickness in these directions. In other words, the lime- 

 stones become thin as the sandstones and shales become thick. 



We may thus regard Derbyshire as a focus of activity from whence 

 the calcareous elements have been propagated with constantly 

 diminishing intensity, at least in the directions here stated. What- 

 ever be the extreme thickness of the Derbyshire limestone, it is 

 apparently not less than 5000 feet, as determined by several mea- 

 sured sections of the Geological Survey, — a bulk of calcareous matter 

 truly astonishing when we regard it in its true aspect as the work 

 of marine animals. iSTowhere else in Britain does the formation 

 attain such vertical dimensions ; but they may possibly be less than 

 those which it reaches in the Rocky Mountains and elsewhere. 

 Traced northwards into Northumberland and Scotland, the lime- 

 stones, as is now well known, dwindle down in thickness as they 

 become more and more mixed with transported sediment, and in 

 Lancashire appear on the point of expiring. 



Traced southwards, the limestone ends against the shelving shore of 

 the old land-surface of the barrier, as at Charnworth Forest (fig. 5) ; 



Fig. 5. — Section of the Oarhoniferous and Triassic Strata lying on the 

 edge of the Cambrian Rocks of Charnwood Forest. 



Charnwood Forest. 

 Grace Diea. 



1. Triassic Breccia. 3. Carboniferous Limestone. 



2. Carboniferous Limestone-shale. 4. Cambrian slate and porphyry. 



or is altogether absent, as in South Staffordshire*, on account of 

 this district having been above the sea, as shown by Mr. Jukes t. 



* Murchison, Proc. Geol. Soc. vol. ii, p. 407. 

 t ' Memoir on the South StaflFordshire Coalfield,' 



2nd edit. 



