of the neighbourhood of Bristol. 215 



basin, containing the bones of birds and fish, but an important differ- 

 ence is that the English strata are destitute of gypsum. 



We sometimes meet with magnesian limestone subordinate to 

 the first flcctz or mountain limestone. Sometime ago I discovered 

 a very beautiful sparry dolomite lying in conformable strata upon 

 the mountain limestone near Ross in Herefordshire. This variety 

 contains 44 per cent, of carbonate of magnesia. A small ridge 

 of rock, about four miles north-west of Bristol, upon which Lord 

 de Clifford's house is built, is entirely composed of a magnesian 

 limestone abounding in shells, entrochi, and madrepores ; and in an 

 adjoining hill which overlooks Blais Castle it occurs, as far as I can 

 understand, interstratified with the mountain limestone. 



A specimen of this variety I find to be composed of 



Carbonate of lime . . . . 



Carbonate of magnesia . . 



Oxyd of iron 



Silica and bituminous matter 

 Loss . 



58 



38 



L 



1.5 

 1.5 









100.0 



I may remark that this magnesian limestone varies remarkably in 

 specimens taken even from contiguous situations, both in colour and 

 other external characters. It is therefore probable that these varieties 

 would afford slight differences in their chemical ingredients. 



I am entirely indebted to Mr. Bright, of Ham Green, for being 

 able to give the last mentioned locality of this rock ; for upon in- 

 forming him of my present pursuit, he desired me to examine the 

 ridge to which I have just alluded, as he conceived it to be com- 

 posed of a magnesian limestone. 



2e2 



