18461856] CLEAVAGE AND FOLIATION 2CX) 



themselves into little curling pieces, and then again into Letter 542 

 crystals of feldspar of large size, and which consequently 

 were all strictly parallel, the series was perfect and 

 beautiful. Apparently also the rounded grains of quartz 

 had in other parts aggregated themselves into crystalline 

 nodules of quartz. [Fig. 7.] 



I have not been able to get Sorby yet, but shall not 

 probably have anything to write on it. I am delighted you 

 have taken up the subject, even if I am utterly floored. 



P.S. I have a presentiment it will turn out that when 

 clay-slate has been metamorphosed the foliation in the resultant 

 schist has been due generally (if not, as I think, always) 

 to the cleavage, and this to a certain degree will " save my 

 bacon" (please look at my saving clause, p. I6/), 1 but [with] 

 other rocks than that, stratification has been the ruling agent, 

 the strike, but not the dip, being in such cases parallel to 

 any adjoining clay-slate. If this be so, pre-existing planes 

 of division, we must suppose on my view of the cause, de- 

 termining the lines of crystallisation and segregation, and not 

 planes of division produced for the first time during the act 

 of crystallisation, as in volcanic rocks. If this should ever be 

 proved, I shall not look back with utter shame at my work. 



To J. D. Hooker. Letter 543 



Down, Sept. 8th [1856]. 



I got your letter of the ist this morning, and a real good 

 man you have been to write. Of all the things I ever heard, 

 Mrs. Hooker's pedestrian feats beat them. My brother is 

 quite right in his comparison of "as strong as a woman," as 

 a type of strength. Your letter, after what you have seen 

 in the Himalayas, etc., gives me a wonderful idea of the 

 beauty of the Alps. How I wish I was one-half or one- 



1 "As in some cases it appears that where a fissile rock has been 

 exposed to partial metamorphic action (for instance, from the irruption of 

 granite) the foliation has supervened on the already existing cleavage- 

 planes ; so, perhaps in some instances, the foliation of a rock may have 

 been determined by the original planes of deposition or of oblique current 

 laminae. I have, however, myself never seen such a case, and I must 

 maintain that in most extensive metamorphic areas the foliation is the 

 extreme result of that process, of which cleavage is the first effect " 

 (Ibid., p. 167). 



VOL. II. 14 



