146 Geological Society. Prof. Sedgwick on the 



bution of fossils even in some of the more fossiliferous divisions, add 

 greatly to the difficulties of establishing true definite groups even 

 within the limits of our island. The difficulties are indefinitely in- 

 creased in comparing the formations of remote continents. But 

 these circumstances are compensated by the magnificent scale of 

 development of the successive groups, and their wide geographical 

 distribution. Taken together, they have a great unity of character ; 

 and even in remote continents they seem to form a common base, 

 from which we may hope to compute the whole series of secondary 

 and tertiary deposits that surmount them." 



Cumbrian groups, exhibited, in ascending order, in a section from 

 Keswick through Kendal to Kirkby Lonsdale : — 



1. The group of Skiddaw Forest, &c, the lower part of which 

 rests on the granite, and passes into a system of crystalline strata 

 resembling the rocks of the first class in North Wales ; the upper 

 part abounds in a fine dark glossy clay slate, interrupted here and 

 there by beds of more mechanical structure. The whole is of great 

 thickness, almost without calcareous matter, and without any trace 

 of organic remains, and forms the mineral axis of the Cumbrian 

 mountains. 



2. A group essentially composed of quartzose and chloritic roof- 

 ing slates alternating with mechanical beds of coarser structure, 

 and also with innumerable igneous rocks (compact felspar, felspar 

 porphyry, brecciated porphyries, &c. &c.) which partake of all the 

 accidents of the slates. It is of enormous thickness, and rises into 

 the highest mountains of the country ; and though chiefly developed 

 on the south side of the preceding group (No. 1), it also appears 

 extensively on the north side of the lower group, which thus forms 

 a mineral axis- — a fact not yet noticed in any of the published geo- 

 logical maps. Though abounding in calcareous matter, it has no 

 organic remains. This group is bounded by calcareous slates, which 

 extend from the south end of Cumberland to the neighbourhood of 

 Shap Wells, and have been described by the author in a former 

 paper. (See Transactions of Geological Society.) 



3. The next group extends from the calcareous slates (above 

 noticed) to the carboniferous rocks, &c. which surround and cut off 

 the older series*. The highest part of the ascending section is 

 shown on a line which descends to the Lune near Kirkby Lonsdale. 

 The other sections are much less perfect. The whole group is sepa- 

 rated, provisionally, into two divisions. • 



The Lower division commences with the calcareous slates above 



* In a geological map lately presented by the author (which professes 

 only to be a copy of a map made by himself nearly twenty years since), 

 he represents all the beds above the calcareous slates of one colour. He 

 does this, because he is unable to fix the demarcations of the several divi- 

 sions of the whole group. As he considered the whole to represent the 

 Silurian system he wished to represent the surface by three colours ; but 

 he found it impossible, even approximately, to represent their boundaries. 

 And even with a simpler system of two divisions, he is unable, at present, 

 to define correctly their line of demarcation ; nearly all the middle portions 

 of the sections being devoid of fossils. 



