I hope you will have a good
illustration or map of the waving line of junction of the slate and
schist with uniformly directed cleavage and foliation. It strikes me as
crucial. I remember longing for an opportunity to observe this point.
All that I say is that when slate and the metamorphic schists occur in
the same neighbourhood, the cleavage and foliation are uniform: of
this I have seen many cases, but I have never observed slate overlying
mica-slate. I have, however, observed many cases of glossy clay-slate
included within mica-schist and gneiss. All your other observations on
the order, etc., seem very interesting. From conversations with Lyell,
etc., I recommend you to describe in a little detail the nature of the
metamorphic schists; especially whether there are quasi-substrata of
different varieties of mica-slate or gneiss, etc.; and whether you
traced such quasi beds into the cleavage slate. I have not the least
doubt of such facts occurring, from what I have seen (and described at
M. Video) of portions of fine chloritic schists being entangled in the
midst of a gneiss district. Have you had any opportunity of tracing a
bed of marble? This, I think, from reasons given at page 166 of my
"S. America," would be very interesting. (539/2. "I have never had an
opportunity of tracing, for any distance, along the line both of strike
and dip, the so-called beds in the metamorphic schists, but I strongly
suspect that they would not be found to extend, with the same character,
very far in the line either of their dip or strike. Hence I am led to
believe that most of the so-called beds are of the nature of complex
folia, and have not been separately deposited. Of course, this view
cannot be extended to THICK masses included in the metamorphic series,
which are of totally different composition from the adjoining schists,
and which are far-extended, as is sometimes the case with quartz
and marble; these must generally be of the nature of true strata"
("Geological Observations," page 166).) A suspicion has sometimes
occurred to me (I remember more especially when tracing the clay-slate
at the Cape of Good Hope turning into true gneiss) that possibly all the
metamorphic schists necessarily once existed as clay-slate, and that
the foliation did not arise or take its direction in the metamorphic
schists, but resulted simply from the pre-existing cleavage. The
so-called beds in the metamorphic schists, so unlike common cleavage
l