900 
tion of North Wales there is no positive zoological distinction in 
the successive descending groups, however vast in thickness or di- 
stinct in mineral structure. It is not by the addition of new species, 
but by the gradual disappearance of the species in the higher groups, 
that the successive groups are zoologically characterized. Below 
the Caradoc sandstone there seems to have been very few new types 
of creation, as far at least as we have learnt from any positive facts 
in the country here described. This conclusion is nearly in accord- 
ance with a statement made by the author in a former paper, viz. 
“The difficulty of classification by organic remains increases as 
we descend, and is at length insurmountable ; for in the lowest 
stratified groups, independently of metamorphic structure, all traces 
of fossils gradually vanish; and the great range of certain species 
through numerous successive groups, and the very irregular distri- 
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 contments. But 
these circumstances are compensated by the magnificent scale of 
development cf 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 
ests 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 
anythe, 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 uf Geclogical Society.) 
3. The next group extends from the calcareous slates. (above 
