1846.] SEDGWICK ON THE SLATE ROCKS OF CUMBERLAND. 107 



III. Upper system of slates, with a few calcareous bands full of 

 fossils, the whole deposit more or less fossiliferous. 



II. Green roofing slate and contemporaneous porphyry, &c. 



1. Skiddaw slate, the lower part of which is metamorphic. 



The superficial extent of these three groups is represented on the 

 maps of Cumberland and Westmoreland which I have had the ho' 

 nour to present to the Society, and the lowermost (I.) has no exact 

 parallel in Wales. The one marked II. is put on the parallel of 

 the Snowdonian slates, but in Cumbria contains no fossils. The 

 next (III.) commences with beds of the age of the Caradoc sand- 

 stone, and ends M'ith rocks obviously of the age of the Upper Lud- 

 low rocks and tilestone of the Silurian system : it therefore includes 

 the whole or nearly the whole of that system. The subdivisions of 

 this great physical group (III.) were described in detail in the paper 

 just alluded to, and were in the following order : — - 



6. A great group nearly parallel with the Upper Ludlow rock, 

 and ending on the banks of the Lune with a red flag or tilestone. 



5. Coarse slates, flags, grits, &c. 



4. Ireleth slates, &c., subdivided into three subordinate groups : 

 viz. 



y. Upper Ireleth slate. 



/3. Calcareous slate and limestone. 



a. Lower Ireleth slate. 



3. Coniston or Furness grits. Thickness greater than No. 2. 



2. Coniston or Brathay flagstone. Thickness 1 500 feet. On the 

 parallel of Wenlock shale. 



1. Coniston limestone, surmounted by calcareous shales and slate. 

 Aggregate thickness about 300 feet. Fossils, Lower Silurian. 



During the past summer I have re-examined a part of the evidence 

 on which I endeavoured to establish these subdivisions of the fossi- 

 liferous slates of Westmoreland, &c., and I still adopt the first four 

 subdivisions almost without change. But No. 5. (coarse slates, flags, 

 grits, &c.) I now consider as forming a sub-group of No. 4, or Ireleth 

 slates, and No. 6. 1 subdivide into two groups, — a lower and an upper. 

 The lower of these two groups passes into the system of the Ireleth 

 slates in the descending sections, and in the ascending sections passes 

 into the upper group, which ends with the tilestone. This slight 

 change I was compelled to adopt when I endeavoured to lay down 

 the subdivisions of the whole fossiliferous series on the county map ; 

 but it is in itself unimportant, and it involves no change of principle. 

 According to this scheme, No. 5, the upper group (on the parallel 

 of the Upper Ludlow rock) is subdivided into — 



h. Arenaceous slates, grits and flags, almost without cleavage, and 

 passing in ascending order into green and red arenaceous flag- 

 stone (tilestone) (c). 

 a. Slates, grits and flags, with partial slaty cleavage, and passing 



into and blending with I of No. 4. 

 No. 4. Ireleth slates, &c., includes 

 ?. Coarse slates, flags and grits, &c. 

 y. Upper Ireleth slates. 



