130 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



and still more emphatically in Cumberland, where the Skiddaw slate 

 is wfthout fossils. 



' Taking the whole view of the case therefore as far as I know it, 

 I would divide the older palaeozoic rocks of our island into three great 

 groups — each (in local descriptions) to be further subdivided. They 

 would then stand thus : — 



3rd, Upper group, or exclusively Upper Silurian. 



2nd, Middle group, or Lower Silurian, including Llandeilo, 



Caradoc, and perhaps Wenlock. 

 1st group, or Cambrian, 



This arrangement does no violence to the Silurian system of Sir 

 R. Murchison, but takes it up in its true place ; and I think that it 

 enables us to classify the old rocks in such a way as to satisfy the 

 conditions both of fossil and physical as well as of mineralogical 

 development. 



The general conclusions which I obtain from the details given in 

 the former paper and the present one are briefly these : — 



The fossiliferous slates, extending from the Coniston limestone to 

 the valley of the Lune, are subdivided into five formations or 

 primary groups. 



5. Coarse slates, generally without transverse cleavage planes, 

 grits, flagstones, &c., divided into three sub-groups. 



y. Greenish-grey and red flagstones (tilestone^. 



/3. Grits and slates without true cleavage planes, with numerous 



Upper Ludlow fossils. 

 a. Coarse slates passing downwards into 4 ^. 



4. A formation of very great thickness (7re/e^^ slates, ^c.), divided, 

 for convenience of description, into four sub-groups: — 



5. Coarse slates and grits, — often passing into the structure of the 



lower sub-groups, and not to be separated from them. 

 y. Upper or great Ireleth slate zone. 

 jG. Upper limestone. 

 a. Lower Ireleth slates. 



Respecting the upper part (^) of this great formation there is no 

 difference of opinion. It contains beds of Terehratula navicnla and 

 several other well-known Lower Ludlow fossils ; and has already 

 been compared, in a general way, with the Lower Ludlow rocks, 

 both by Mr. Sharpe and myself. 



3. A great deposit of hard gritty beds, sometimes even approach- 

 ing a conglomerate form, with subordinate slaty masses, and with 

 numerous large spherical concretions arranged parallel to the beds. 

 The fossils are very rare in this group, but among them are Grap- 

 tolites ludensis, Cardiola interrupta, Orthoceras ibex and O. svbun- 

 dulatum. All the species are Upper Silurian. 



2. Coniston Br athay flagstone. Thickness roughly computed at 

 1500 feet. Its most characteristic fossils are Graptolites ludensis, 



