from Penigent to Kirkhy Stephen. 99 



The whole series of strata composing- the mountains along the line of sec- 

 tion may be divided into three great natural groups : 1st, The Scar limestone. 

 2nd, All the alternating subordinate groups (from No. 2. to No 12. inclusive), 

 ending with the great upper shale over the twelve-fathom limestone. 3rd, All 

 the various deposits (from No. 13. to No. 17. inclusive) associated with mill- 

 stone grit*. 



The lowest of these groups is almost identical with the formation of moun- 

 tain limestone at the base of the carboniferous series of Derbyshire and the 

 Bristol Channel. The middle group has, on the contrary, little in common 

 with the carboniferous series of Derbyshire, and, perhaps, still less with that 

 of the Bristol Channel : but it conforms very nearly to a portion of the car- 

 boniferous system in the chain of Cross Fell. The third group appears in 

 some form or other through the whole extent of the carboniferous chain ; and, 

 though by no means constant in its characters, undergoes perhaps less modi- 

 fication in its long range than either of the other two. 



A fourth great group might include all the richest deposits of our northern, 

 midland, and south-western coal-fields ; and the analogies they present both 

 in structure and position are obvious ; but they belong not to the subjects 

 considered in this paper. 



In the North of England the deposit of mountain limestone was exposed to 

 many interruptions, arising from drift, mud and sand, mixed with the wreck 

 of numerous trees and plants. Upon such masses as these, encrinites and 

 corals would obviously refuse to grow, till the incoherent sediment became 

 compacted by calcareous matter, upon which they would again find an appro- 

 priate resting-place. The calcareous beds would then go on increasing till 

 they were again interrupted by a new incursion of mud and sand. Effects 

 like these were many times repeated. 



In the valley of the Tweed these disturbing forces were in full action from 

 the first commencement of the deposit of mountain limestone; — in Yorkshire 

 (as appears from the previous details) they produced very considerable effects 

 long before the complete development of the formation ; — in Derbyshire, and 

 in the south-western coal-fields, on the contrary, they produced but a small 

 modification of the carboniferous system before the deposit of mountain lime- 

 stone was completed. 



I hope in a subsequent paper to describe several similar modifications of 

 structure in the northern calcareous zone of the Cumbrian mountains. 



2. Many of the coal-beds above described must have been deposited under 



* The three longitudinal sections, fig. 2. 3. and 4, are coloured on this principle, the detailed 

 subdivisions appearing only in fig. 1. 



o 2 



