SEDGWICK ON THE ROCKS OF N. WALES AND CUMBERLAND. 449 



The author next alludes to the rocks of Howgill Fell and Raven - 

 stonedale on the east side of the valley of the Lune ; and he con- 

 siders that these rocks, which offer considerable difficulties in their 

 accurate determination, though separated by great faults from the 

 higher parts of the Upper Ludlow series, are not to be considered 

 as unconformable to that series, and probably contain a portion of jt 

 in their great folds and undulations. Through the eastern boundary 

 of the district in which they occur, ranges the great Craven fault, 

 described by the author in a former paper ; and he has found, 

 brought up apparently on one side of the fault, and appearing in 

 the hills between Dent and Sedbergh and between Sedbergh and 

 Ravenstonedale, a series of calcareous shales containing fossils, 

 which mark the date of the series as not far from the parallel of 

 the Coniston limestone ; but he believes with Mr. Sharpe, that the 

 greater part of Howgill Fells is made up of the coarse gritty 

 Upper Silurian beds between the Ireleth slates and the Upper 

 Ludlow rocks. 



Returning then to the comparison which was the great object of 

 his communication, the author states as his general result, — 



1st. That the chlorite and mica slates of Caernarvon and 

 Anglesea have no parallel in Cumberland, being of a distinct epoch 

 from the other rocks in the district, and evidently older. The 

 same cannot be said of the metamorphic and crystalline rocks of 

 Skidclaw forest, which rest on the granite, and pass gradually into 

 the coarse Skiddaw slate. These may have assumed their present 

 structure after the epoch of the Skiddaw slates. 



Of the Skiddaw slate also, the author finds no exact represent- 

 ative in North Wales. It is not traversed by contemporaneous 

 beds of porphyry, &c. Though composed of a fine, dark, glossy 

 clay slate alternating with coarse bands, (sometimes, though rarely, 

 passing into very coarse grit,) and though containing in one or 

 two places a quantity of carbonaceous matter, it does not effervesce 

 with acids, and no fossils have yet been obtained from it. Should 

 fossils be discovered in it, they must belong to some of the oldest 

 Protozoic types of our island. 



2. That the green slates and porphyries of Cumberland cannot 

 be separated from the rocks of the same mineral structure in 

 Snowdonia. One, however, contains bands of fossils, and the other 

 does not. The porphyries abound so much in Cumbria, that 

 organic beings were unable to exist among them, or their remains 

 have become obliterated. 



3. The Coniston limestone represents the top of a series which 

 passes into the Creseis and Graptolite flagstone, and so also does 

 the Llansaintffraid limestone. The list of fossils from these two 

 groups is also nearly identical, and they both contain some Wen- 



(2.) The beds of old red conglomerate on the Lune are not exactly parallel 

 to the beds of " tilestone." 



(3.) The conglomerates contain many fragments of the "tilestone," which 

 must have been solid before the conglomerates were formed. 



H H 3 



