h I enjoy speaking to any one
upon subjects which I am always thinking about, but never have any one
to talk to [about]. After leaving the Falklands we proceeded to the
Rio S. Cruz, following up the river till within twenty miles of the
Cordilleras. Unfortunately want of provisions compelled us to return.
This expedition was most important to me as it was a transverse section
of the great Patagonian formation. I conjecture (an accurate examination
of fossils may possibly determine the point) that the main bed is
somewhere about the Miocene period (using Mr. Lyell's expression); I
judge from what I have seen of the present shells of Patagonia. This bed
contains an ENORMOUS field of lava. This is of some interest, as being a
rude approximation to the age of the volcanic part of the great range of
the Andes. Long before this it existed as a slate and porphyritic
line of hills. I have collected a tolerable quantity of information
respecting the period and forms of elevations of these plains. I think
these will be interesting to Mr. Lyell; I had deferred reading his third
volume till my return: you may guess how much pleasure it gave me; some
of his woodcuts came so exactly into play that I have only to refer to
them instead of redrawing similar ones. I had my barometer with me,
I only wish I had used it more in these plains. The valley of S. Cruz
appears to me a very curious one; at first it quite baffled me. I
believe I can show good reasons for supposing it to have been once a
northern straits like to that of Magellan. When I return to England you
will have some hard work in winnowing my Geology; what little I know I
have learnt in such a curious fashion that I often feel very doubtful
about the number of grains [of value?]. Whatever number they may turn
out, I have enjoyed extreme pleasure in collecting them. In T. del Fuego
I collected and examined some corallines; I have observed one fact which
quite startled me: it is that in the genus Sertularia (taken in its
most restricted form as [used] by Lamoureux) and in two species which,
excluding comparative expressions, I should find much difficulty in
describing as different, the polypi quite and essentially differed in
all their most important and evident parts of structure. I have already
seen enough to be convinced that the present families of corallines as
arranged by Lamarck, Cuvier, etc., are highly artificial. It appears
that they are in the same state [in] which shel