THE CUMBRIAN GROUP. 459 



Lake district extending from the Coniston Limestone to the 

 valley of the Lune, are divided into five formations. 



, f c. Greenish Grey and Red Flagstones. 



vP er , , b. Grits and Slates, with Upper Ludlow Fossils. 



[ a. Coarse Slates passing into No. 4, d. 

 ( d. Coarse Slates, Flags, and Grits, with Terebratula 



navicula, and Upper Ludlow Fossils. 

 4. Ireleth Slates . . -j c. Upper Ireleth Slates. 



b. Calcareous Slates and Limestones. 

 { a. Lower Ireleth Slates. 

 3. Coniston Grit . . Graptolithus, Cardiola, Ch'thoceras. 



Gra P tolithus and U PP er Silurian S P ecies ' 



"Whether the Cambrian and Cumbrian rocks, which we 

 have described above from Professor Sedgwick's researches, 

 form a distinct system, or only a portion of the Silurian 

 group, we have not at present sufficient data to enable us to 

 determine ; we have therefore placed them in a separate 

 section at the close of the present chapter. So much has 

 been done by our distinguished countrymen, Murchison and 

 Sedgwick, in the department of Palaeozoic geology, that we 

 have still much to hope from their further researches into this 

 most ancient epoch of the earth's history. D'Orbigny de- 

 scribes 845 species of animals from the Silurian system, of 

 which 418 belong to the upper, and 427 to the lower 

 divisions. Of the 418 upper Silurian species, 356 are 

 Mollusca, and 61 are Eadiata; of the 427 lower Silurian 

 species, 375 belong to the Mollusca, and 52 to the Eadiata. 

 The Silurian system of, Bohemia has, for the last ten years, 

 engaged the attention of M. Barrande, who has discovered 

 the astonishing number of 1100 species of invertebrata in 

 the Silurian rocks of that region ; whereas, from the same 

 area, about 20 species only had been previously described. 

 Of the 1100 species he finds : 



Crustacea, chiefly Trilobites .... 250 species. 



Cephalopoda ....... 250 



Gasteropoda and Pteropoda . . . .160,, 



Conchifera ....... 130 



Brachiopoda ....... 200 



Zoophyta ........ 110 



1100 



