G78 



phfenomena that terminate in ordinary volcanic action. Elevatory 

 forces, when considered in this general way, explain the phsenomena 

 of strike — the parallelism of great contemporaneous elevations — as 

 well as the exceptions to the rule of parallelism. 



GROUPS OF THE CUMBRIAN SECTION, &C. 



The author then commences the separation of the whole series of 

 rocks of the second class into natural groups, founded on sections ex- 

 hibited in the several districts above noticed ; and after shortly dis- 

 cussing two sections connecting the Cheviot hills with the formations 

 in the basin of the Tweed, he describes in some detail a transverse 

 section through the whole system of the Cumbrian mountains, which 

 exhibits the following groups in ascending order. 



(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 ; 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, al- 

 most 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 igneousrocks (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 geological maps. 

 Though abounding in calcareous matter, it has no organic remains. 

 (Lower Cambrian system). 



(3.) A great series, expanded through Westmoreland and parts of 

 Lancashire and Yorkshire. Itis based on calcareous slates, passing into 

 limestone, and full of organic remains, and in its lower division are fine 

 roofing slates, but less crystalline than those of the preceding group. 

 Its upper division (not however separable by any very distinct zoologi- 

 cal or mineralogical characters from the lower) abounds in arenaceous 

 flagstone, coarse quartzose greywacke, coarse slates with imperfect 

 cleavage, and not fit for use, and the series is incomplete, being cut 

 off by the unconformable deposits of old red sandstone and carboni- 

 ferous limestone. Distinct beds of limestone are almost wanting in 

 this upper division, and organic remains are very rare, but they ap- 

 pear here and there in very thin bands among the coarse siliceous 

 slates. Provisionally, the lower division is placed in the Upper 

 Cambrian system, and the upper division in the Silurian system ; but 

 without being separable into any further clear subdivisions. This 

 great group (No. 3.) does not appear on the north side of the 

 mineral axis of Cumberland, as was represented in the early geolo- 

 gical maps. 



