638 Professor Sedgwick and R. I. Murchison, Esq., on the 



regions. Before this can be effected, much no doubt remains to be done. We 

 possess large materials, bearing on these questions, which have as yet been very 

 imperfectly examined. All we can do at present is, to make a first approxima- 

 tion to the solution of these difficult questions. That they press upon us for 

 an answer cannot be doubted, when we consider that no one has yet attempted 

 any rigid comparison between the older rocks of Cumberland, Wales, and 

 Devonshire ; that the antiquity of the slate rocks of Devonshire and Cornwall 

 has generally been estimated by their mineral characters or by their vicinity 

 to the granite — means which are not merely inconclusive, but often lead to 

 conclusions which are absolutely false; and lastly, that the culmiferous series 

 (occupying more than one-third of the whole superficial extent of Devon- 

 shire) has, under the name of greywacke, been confounded with formations, 

 to some of which, at least, it bears no analogy, either in position, mineral 

 structure, or organic remains. 



Chap. II. — Successive Deposits between the North Coast of Devon and 

 the Culmiferous Series. 



Before we attempt any description or classification of these several deposits, 

 we think it expedient to give a general account of their extent, and the places 

 they occupy in the actual sections of the country. It will be seen, that our bound- 

 ary lines (Map, PI. L.) inclose a small portion of the north-west corner of So- 

 mersetshire, which is too intimately connected with our second region to be 

 entirely overlooked. Our examination commenced with the northern part of the 

 Quantock Hills, which, although beyond the limits of the country indicated in 

 the preceding portion of the paper, must also be briefly noticed. The north- 

 eastern flanks of these hills are composed of a soft, unctuous slate, not un- 

 usually of a red colour, here and there highly calcareous, and sometimes passing 

 into thick, irregular masses of limestone partaking of the prevailing colours of 

 the neighbouring rock*. From beneath these, rises a system of be^s which oc- 

 cupies the central and higher portions of the hills, and (as far as we could make 

 out, from our hasty examination of a country so much covered with vegeta- 

 tion) is composed of hard, and sometimes coarse sandstone, alternating with 

 more fissile, micaceous masses of finer structure, and with masses of soft, 

 rotten slate, resembling the prevailing rocks of the upper group above de- 



* In the language of the workmen, the thick beds of red limestone are called trug ; and the 

 thinner beds, after passing into a soft, glossy, unctuous slate, are called pavey. The soft, earthy 

 slates generally pass, in Devonshire, under the name of shillat. 



