modore
has gone there, and in the hurry has carried our letters with him;
perhaps amongst them there will be one from you. I wish I had the old
Commodore here, I would shake some consideration for others into his old
body. From Coquimbo you will again hear from me.

LETTER 7. TO J.S. HENSLOW. Lima, July 12th, 1835.

This is the last letter which I shall ever write to you from the shores
of America, and for this reason I send it. In a few days time the
"Beagle" will sail for the Galapagos Islands. I look forward with joy
and interest to this, both as being somewhat nearer to England and for
the sake of having a good look at an active volcano. Although we have
seen lava in abundance, I have never yet beheld the crater. I sent by
H.M.S. "Conway" two large boxes of specimens. The "Conway" sailed the
latter end of June. With them were letters for you, since that time I
have travelled by land from Valparaiso to Copiapo and seen something
more of the Cordilleras. Some of my geological views have been,
subsequently to the last letter, altered. I believe the upper mass
of strata is not so very modern as I supposed. This last journey has
explained to me much of the ancient history of the Cordilleras. I feel
sure they formerly consisted of a chain of volcanoes from which enormous
streams of lava were poured forth at the bottom of the sea. These
alternate with sedimentary beds to a vast thickness; at a subsequent
period these volcanoes must have formed islands, from which have been
produced strata of several thousand feet thick of coarse conglomerate.
(7/1. See "Geological Observations on South America" (London, 1846),
Chapter VII.: "Central Chile; Structure of the Cordillera.") These
islands were covered with fine trees; in the conglomerate, I found one
15 feet in circumference perfectly silicified to the very centre. The
alternations of compact crystalline rocks (I cannot doubt subaqueous
lavas), and sedimentary beds, now upheaved fractured and indurated, form
the main range of the Andes. The formation was produced at the time when
ammonites, gryphites, oysters, Pecten, Mytilus, etc., etc., lived. In
the central parts of Chili the structure of the lower beds is rendered
very obscure by the metamorphic action which has rendered even the
coarsest conglomerates porphyritic. The Cordilleras of the Andes so
worthy of admiration from the grandeur of their dimensions, rise in
dignity when it is considered that since the period of a