482 Ruskin — Brecciated Formations. 



a liquid or vapovir in cavities of rocks, and which I shall call 

 " accrete." 



The fluor nodnles of Derbyshire, and amethystine nodules of 

 some trap rocks, present, in their interiors, the most beautiful 

 phenomena of concrete crystallization, of which I hope to give 

 careful drawings. 



It is true, as I said in the last paper, that these two processes are 

 perpetually associated, and also that the difference between them is 

 sometimes only between coats attracted and coats imposed. A small 

 portion of organic substance will, perhaps, attract silica to itself, out 

 of a rock which contained little silica in proportion to its substance ; 

 and this first knot of silica will attract more, and, at last, a large 

 mass of flint will be formed, which I should call " concrete ;" but if 

 a successive overflowing of a silicious spring had deposited succes- 

 sive layers of silica upon it, I should call it " accrete." But the 

 resemblance of the two processes in such instances need not inter- 

 fere with the clearness of our first conception of them ; nor with 

 our sense of the firm distinction between the separation of a solid 

 mass, already formed, into crystals or coats in its interior substance, 

 and the increase of crystalline or coated masses by gradual impo- 

 sition of new matter. 



Now let me re-state the scope of the questions, for the following 

 out of which I want to collect materials : — 



I. I suspect that many so-called " conglomerates" are not conglo- 

 merates at all, but concretionary formations, capable, finally, of 

 complete mechanical separation of parts ; and therefore that even 

 some states of apparently rolled gravel are only dissolutions of 

 concretionary rock. 



Of course, conglomerates, in which the pebbles are fragments 

 of recognizable foreign rocks, are beyond all possibility of chal- 

 lenge ; as also those in which the nodules could not, by any chemis- 

 try, have been secreted from the surrounding mass. But I have in 

 my hand, as I write, a so-called "conglomerate" of red, rounded, flint 

 "pebbles," much divided by interior cracks, enclosed by a finely 

 crystallized quartz ; and I am under the strongest impression that 

 the enclosed pieces are not pebbles at all ; but secretions — the 

 spots on a colossal bloodstone. It is with a view to the solution of 

 this large question, that I am examining the minor structure of 

 brecciated agates and flints. 



II. It seems to me that some of the most singular conditions of 

 crystalline metamorphic rocks are the result of the reduction of true 

 conglomerates into a solid mass ; and I want therefore to trace the 

 changes in clearly recognizable conglomerates, where they are affected 

 by metamorphism ; and arrange them in a consistent series. 



III. I cannot, at present, distinguish in rocks the faults, veins, and 

 brecciations, caused by slow contraction, from those occasioned by 

 external pressure or violence. It seems to me now that many dis- 

 tortions and faults, which I have been in the habit of supposing the 

 result of violence, are only colossal phenomena of retraction or con- 

 traction ,• and even that many apparent strata have been produced by 



