206 GEOLOGY [CHAP. IX 



Letter 541 to the cleavage of the clay-slate, but of course with different 

 dip (excepting in those rare cases when cleavage and stratifi- 

 cation are parallel). Having this difficulty before my eyes, I 

 was much struck with MacCulloch's statement (p. 166 of 

 my v$\ America] about marble in the metamorphic series not 

 forming true strata. 



Your expectation of the metamorphic schists sending veins 

 into neighbouring rocks is quite new to me ; but I much doubt 

 whether you have any right to assume fluidity from almost 

 any amount of molecular change. I have seen in fine volcanic 

 sandstone clear evidence of all the calcareous matter travelling 



o 



at least /j.J ft. in distance to concretions on either hand (p. 113 

 of 6\ America). 1 I have not examined carefully, from not 

 soon enough seeing all the difficulties ; but I believe, from 

 what I have seen, that the folia in the metamorphic schists 

 (I do not here refer to the so-called beds) are not of great 

 length, but thin out, and are succeeded by others ; and the 

 notion I have of the molecular movements is shown in the 

 indistinct sketch herewith sent [Fig. 6]. The quartz of 

 the strata might here move into the position of the folia 

 without much more movement of molecules than in the 

 formation of concretions. I further suspect in such cases as 

 this, when there is a great original abundance of quartz, 

 that great branching contemporaneous veins of segregation 

 (as sometimes called) of quartz would be formed. I can 

 only thus understand the relation which exists between the 

 distorted foliation (not appearing due to injection) and the 

 presence of such great veins. 



I believe some gneiss, as the gneiss-granite of Humboldt, 

 has been as fluid as granite, but I do not believe that this is 

 usually the case, from the frequent alternations of glossy clay 

 and chlorite slates, which we cannot suppose to have been 

 melted. 



I am far from wishing to doubt that true sedimentary 

 strata have been converted into metamorphic schists : all 



1 " Some of these concretions (flattened spherical concretions com- 

 posed of hard calcareous sandstone, containing a few shells, occurring in 

 a bed of sandstone) were 4 ft. in diameter, and in a horizontal line 9 ft. 

 apart, showing that the calcareous matter must have been drawn to the 

 centres of attraction from a distance of four feet and a half on both 

 sides" (Geological Observations on S. America, p. 113). 



