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 vS\ 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 

 at least 4J ft. in distance to concretions on either hand (p. 113 

 of .S. 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). 



