SEDGWICK ON THE ROCKS OF N. WALES AND CUMBERLAND. 443 



The whole series of the Cumbrian slates, like that of North 

 Wales, has been considered to admit of three primary divisions, but 

 hitherto the separation has been chiefly made from a consideration 

 of physical characters and superposition, and without reference to 

 fossils ; the uppermost only of the three being supposed to contain 

 them. In this state the author left his maps in 1824, and they 

 show the superficial extent of the igneous and intrusive rocks, of 

 the lowest or Skiddaw slate, of the great mountain masses of green 

 roofing slate and porphyry, alternating in vast parallel bands, and 

 lastly, of the fossiliferous slates extending from the Coniston lime- 

 stone to the highest beds on the banks of the Lune, near Kirby 

 Lonsdale. 



Of these beds the author considers that the Skiddaw slate has, 

 perhaps, no true equivalent in N. Wales, and that the green slates 

 and porphyries are probably the exact representatives of a portion 

 of the great system of Snowdonian slates. The Snowdonian slates, 

 however, contain fossils, and the green slates and porphyries 

 of Cumberland are without them ; a difference accounted for as 

 the consequence of the greater abundance of igneous rocks among 

 the green Cumbrian slates. It remains then to find the equivalent 

 of the fossiliferous rocks in the third and highest division of the 

 Cumbrian slates, and for this purpose the author discusses in its 

 most limited form the following questions, namely : — Into what 

 groups may we subdivide the slates expanded between the Co- 

 niston limestone, and the highest beds of the series on the banks 

 of the Lune, near Kirby Lonsdale ? and what are their equiva- 

 lents in North Wales ? Professor Sedgwick considers that, with 

 the exception of the Coniston limestone, and two or three hundred 

 feet of slate and shales surmounting it, the whole of the upper 

 series is Upper Silurian, and in the parallel of the Denbigh flag- 

 stone, using this latter term in its most extended sense. 



The author then enters into some detail with regard to the 

 actual working out of the geology of this district, and his ultimate 

 discovery that a great movement of the strata had brought up the 

 Coniston limestone a second time, on the south side of the estuary 

 of the Duddon, in a ridge called High Haulme, N. W. of Dalton 

 in Furness. In this ridge the beds are nearly vertical, and are 

 associated with trappean rocks and porphyries exactly like those 

 under the Coniston limestone on the north side of the Duddon, 

 which are several miles distant. 



The calcareous bands of this ridge being nearly in the same line 

 with a second or higher band of limestone, became confounded 

 with it, and this has led to a wrong estimate of the geological equi- 

 valents of the second band of limestone. The mistake being cor- 

 rected, it appears that the successive groups of strata will easily 

 fall into their right places without the intervention of any great 

 unconformable overlap. Thus the fossiliferous slates present — first, 

 the Lower Silurian rocks in a very degenerate form ; and secondly, 

 the Upper Silurians in a noble series, more complete and far thicker 

 than the Denbigh flagstones, and ending with the red flags or tile 



