Mr. Warburton o« Magnesian Breccia. 207 



Hills of which I knew the nature, and which very much resembled 

 those from the banks of the Avon, I had no difficulty in ascertaining 

 that the cement of the latter was composed of magnesian limestone ; 

 of which indeed the characters are so strongly marked as to be 

 evident on mere inspection. This breccia consisted of rolled frag- 

 ments of milk white quartz, and of angular fragments of limestone 

 and sandstone such as are found in the neighbouring inclined strata 

 cemented together by yellow magnesian carbonate of lime ; the 

 cement being in great excess. I must refer to Mr. Bright's paper 

 (which I understand will soon be published) for the further descrip- 

 tion of this rock. 



Shortly before seeing the rocks of Hung-road, I had been with the 

 late Smithson Tennant, Esq. to examine the magnesian breccia which 

 he had observed on the Mendip Hills near to the celebrated cliffs of 

 Cheddar. The southern declivity of that limestone chain is there 

 deeply furrowed by wide and extensive combs, in which immense 

 blocks of the breccia many yards in diameter are found lying upon 

 the surface of the limestone. The strata of limestone dip to the 

 south under an alluvial valley, by which they are separated from a 

 low chain of red marl that is found at the distance of about half a 

 mile to the south. 



The breccia of the Mendip Hills very much resembles the breccia 

 from the Avon, consisting of fragments of limestone, magnesian lime- 

 stone, and sandstone cemented together by a yellow magnesian car- 

 bonate of lime ; but I never discovered in it any of the quartz pebbles 

 which are imbedded in the breccia from the Avon. 



Until I had seen the breccia at Hung-road I was unable to account 

 for the presence of these immense insulated blocks upon the sides of 

 the Mendip ; but I have since ventured to conjecture that they once 

 formed a subordinate bed in the strata of red marl which are found 



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