MOUNTAIN LIMESTONE. 



91 



rise southerly from 45^ to 60^. When I visited these hills in 1811, 

 I was forcibly struck with the appearance and elevation of the strata, 

 and I was disposed to attribute their position to the disturbing force 

 which had elevated the granitic range of Charnwood ; but such opin- 

 ions were at that time much discouraged by English geologists. I 

 visited these quarries again in 1830, after having repeatedly observed 

 similar effects produced in the proximity of granite, and I was con- 

 firmed in my former views. 



The theory of Von Buch respecting the conversion of common 

 limestone into magnesian limestone by the proximity to porphyry 

 (sec Chap. XL), maybe considered as deriving some support from 

 the near approach of this magnesian limestone to the porphyry and 

 porphyritic sienite of Charnwood. I shall refer to the subject else- 

 where. The reason for entering more into detail, respecting the 

 magnesian limestone of Bredon and Cloud's Hill than may appear 

 consistent with an introductory work, is, that the strata of the latter 

 hill present an anomalous appearance, which I have not observed 

 elsewhere, and which is connected with the enquiry respecting the 

 character of stratified rocks. At Cloud's Hill, the face of the rock 

 which is worked, rises to the height of about 300 feet. The strati- 

 fication is most distinctly marked by regular strata seams, or partings, 

 which show the elevation of the strata to be about 60'^. In the 

 midst of these strata there are masses in which all traces of stratifi- 

 cation are obliterated ; these masses are not separated by any part- 

 ings or divisions whatever from the strata which surround them ; the 

 masses and strata are precisely of the same quality, and similar in 

 appearance. The masses are more difficult to work because they 

 have no regular partings ; these masses are, on this account, called, 

 by the quarrymen, knobs. The annexed cut represents one of these 

 masses — 



a a, strata of limestone ; J, an unstratified knob. 



Instances of unstratified beds and masses of one kind of rock, in- 

 terposed between regular strata of another kind, are not uncommon ; 

 and in the midst of primary rocks, divided by regular cleavages, parts 

 may be frequently seen, in which the cleavages or divisions are ob- 

 literated ; but, in both these cases, the solution of the cause of this 

 obhteration may be found in igneous fusion, combined with refrigera- 



