18461856] CLEAVAGE AND FOLIATION 2O5 



is very odd, but I suspect that great metamorphic areas are Letter 540 

 generally derived from the metamorphosis of clay-slate, and 

 not from alternating layers of ordinary sedimentary matter. 

 I think you have exactly put the chief difficulty in its 

 strongest light viz. what would be the result of pure or 

 nearly pure layers of very different mineralogical composition 

 being metamorphosed ? I believe even such might be con- 

 verted into an ordinary varying mass of metamorphic schists. 

 I am certain of the correctness of my account of patches of 

 chlorite schists enclosed in other schist, and of enormous 

 quartzose veins of segregation being absolutely continuous 

 and contemporaneous with the folia of quartz, and such, I 

 think, might be the result of the folia crossing a true stratum 

 of quartz. I think my description of the wonderful and 

 beautiful laminated volcanic rocks at Ascension would be 

 worth your looking at. 1 



To C. Lyell. Letter 541 



Down, Jan. I4th [1855]. 



We were yesterday and the day before house-hunting, so 

 I could not answer your letter. 1 hope we have succeeded in 

 a house, after infinite trouble, but am not sure, in York Place, 

 Baker Street. 



I do not doubt that I either read or heard from Sharpe 

 about the Grampians ; otherwise from my own old suspicion 

 I should not have inserted the passage in the manual. 



The laminated rocks at Ascension are described at p. 54. 2 



As far as my experience has gone, I should speak only of 

 clay-slate being associated with mica-slate, for when near the 

 metamorphic schists I have found stratification so gone that 

 I should not dare to speak of them as overlying them. With 

 respect to the difficulty of beds of quartz and marble, this 

 has for years startled me, and I have longed (since I have felt 

 its force) to have some opportunity of testing this point, for 

 without you are sure that the beds of quartz dip, as well as 

 strike, parallel to the foliation, the case is only just like true 

 strata of sandstone included in clay-slate and striking parallel 



Geological Observations on S. America, pp. 166, 167 ; also Geological 

 Observations on the Volcanic Islands, Chap. III. (Ascension), 1844. 



Volcanic Islands, p. 54. " Singular laminated beds alternating with 

 and passing into obsidian." 



