true strata.

(FIGURE 6.)

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 4 1/2 feet in distance to
concretions on either hand (page 113 of "S. America") (541/2. "Some
of these concretions (flattened spherical concretions composed of hard
calcareous sandstone, containing a few shells, occurring in a bed of
sandstone) were 4 feet in diameter, and in a horizontal line 9 feet
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," page 113).) 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 [Figure 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 I can say is, that in the three
or four great regions, where I could ascertain the relations of the
metamorphic schists to the neighbouring cleaved rocks, it was impossible
(as it appeared to me) to admit that the foliation was due to aqueous
deposition. Now that you intend agitating the subject, it will soon be
cleared up.

LETTER 542. TO C. LYELL. 27, York