48 Prof. Sedgwick on the general Structure 



From some of the ridges in the range of Cross Fell, the eye takes in, at 

 one view, the greatest part of the northern calcareous zone. Seen from that 

 distance, all its minor inequalities disappear, and I have often fancied that it 

 resembled a portion of a great semicircular redoubt formed near the base of 

 the older hills, and presenting a long, sweeping, irregular glacis towards the 

 valley of the Eden. On a nearer approach, an illusion of this kind must ne- 

 cessarily vanish, and I only mention it in this place to convey a general idea 

 of the external characters of the district, and of the relations of the great 

 formations to each other. 



On the eastern side of the region, where the older rocks abut, as above 

 described, against the great central calcareous chain, the contrast of external 

 forms is perhaps still more striking. The calcareous mountains, though some- 

 times cut down into mural precipices, and having individual features of the 

 greatest beauty, and, though rising to such an elevation as to overlook the 

 more ancient formations in their immediate neighbourhood, seldom exhibit 

 any grandeur of outline, and in consequence of the horizontal position of their 

 beds, often terminate in great featureless and somewhat tabular masses. On 

 the contrary, the greywacke hills on the confines of Yorkshire and West- 

 moreland have their sides worn down into deep combes and irregular sinuosi- 

 ties, and sometimes rise into sharp angular crests, forming outlines of great 

 variety and beauty. 



Within the calcareous zone above described are several extensive masses 

 of granite, syenite, and porphyry ; but the greatest part of the region is occu- 

 pied by stratified deposits of a slaty texture, which may be subdivided into 

 four distinct formations. 1st, Various crystalline slates, resting immediately 

 on the granite of Skiddaw Forest, and forming the base of the whole stratified 

 series. 2nd, Black glossy clay-slate, sometimes passing into greywacke, but 

 containing no calcareous beds, and no organic remains. 3rd, Green quartzose 

 roofing slate, associated, in every variety of complication, with felspathic rocks 

 of porphyritic structure. This formation contains many beds effervescing 

 briskly when first plunged in acids ; but it contains no continuous bed de- 

 serving the name of limestone, and no organic remains. 4thly, Greywacke 

 slate, often more or less calcareous, and having subordinate beds passing into 

 impure limestone, full of organic remains. 



We owe our first accurate knowledge of these subdivisions to Mr. J. Otley 

 of Keswick, who not merely described them in general terms, but gave their 

 geographical distribution with a very near approximation to accuracy*. 



* See an early Number of the " Lonsdale Magazine," and " A Guide to the English Lakes," by 

 Jonathan Otley of Keswick. 



