CHARLES DARWIN TO MISS S. DARWIN.
Valparaiso, April 23, 1835.

My dear Susan,

I received, a few days since, your letter of November; the three letters
which I before mentioned are yet missing, but I do not doubt they will come
to life. I returned a week ago from my excursion across the Andes to
Mendoza. Since leaving England I have never made so successful a journey;
it has, however, been very expensive. I am sure my father would not regret
it, if he could know how deeply I have enjoyed it: it was something more
than enjoyment; I cannot express the delight which I felt at such a famous
winding-up of all my geology in South America. I literally could hardly
sleep at nights for thinking over my day's work. The scenery was so new,
and so majestic; everything at an elevation of 12,000 feet bears so
different an aspect from that in a lower country. I have seen many views
more beautiful, but none with so strongly marked a character. To a
geologist, also, there are such manifest proofs of excessive violence; the
strata of the highest pinnacles are tossed about like the crust of a broken
pie.

I crossed by the Portillo Pass, which at this time of the year is apt to be
dangerous, so could not afford to delay there. After staying a day in the
stupid town of Mendoza, I began my return by Uspallate, which I did very
leisurely. My whole trip only took up twenty-two days. I travelled with,
for me, uncommon comfort, as I carried a BED! My party consisted of two
Peons and ten mules, two of which were with baggage, or rather food, in
case of being snowed up. Everything, however, favoured me; not even a
speck of this year's snow had fallen on the road. I do not suppose any of
you can be much interested in geological details, but I will just mention
my principal results:--Besides understanding to a certain extent the
description and manner of the force which has elevated this great line of
mountains, I can clearly demonstrate that one part of the double line is of
an age long posterior to the other. In the more ancient line, which is the
true chain of the Andes, I can describe the sort and order of the rocks
which compose it. These are chiefly remarkable by containing a bed of
gypsum nearly 2000 feet thick--a quantity of this substance I should think
unparalleled in the world. What is of much greater consequence, I have
procured fossil shells (from an elevation of 12,000 feet). I think an
examination of these will give an approximate age to these mountains, as
compared to the strata of Europe. In the other line of the Cordilleras
there is a strong presumption (in my own mind, conviction) that the
enormous mass of mountains, the peaks of which rise to 13,000 and 14,000
feet, are so very modern as to be contemporaneous with the plains of
Patagonia (or about with the UPPER strata of the Isle of Wight). If this
result shall be considered as proved (The importance of these results has
been fully recognised by geologists.), it is a very important fact in the
theory of the formation of the world; because, if such wonderful changes
have taken place so recently in the crust of the globe, there can be no
reason for supposing former epochs of excessive violence. These modern
strata are very remarkable by being threaded with metallic veins of silver,
gold, copper, etc.; hitherto these have been considered as appertaining to
older formations. In these same beds, and close to a goldmine, I found a
clump of petrified trees, standing up right, with layers of fine sandstone
deposited round them, bearing the impression of their bark. These trees
are covered by other sandstones and streams of lava to the thickness of
several thousand feet. These rocks have been deposited beneath water; yet
it is clear the spot where the trees grew must once have been above the
level of the sea, so that it is certain the land must have been depressed
by at least as many thousand feet as the superincumbent subaqueous deposits
are thick. But I am afraid you will tell me I am prosy with my geological
descriptions and theories...

Your account of Erasmus' visit to Cambridge has made me long to be back
there. I cannot fancy anything more delightful than his Sunday round of
King's, Trinity, and those talking giants, Whewell and Sedgwick; I hope
your musical tastes continue in due force. I shall be ravenous for the
pianoforte...

I have not quite determined whether I will sleep at the 'Lion' the first
night when I arrive per 'Wonder,' or disturb you all in the dead of night;
everything short of that is absolutely planned. Everything about
Shrewsbury is growing in my mind bigger and more beautiful; I am certain
the acacia and copper beech are two superb trees; I shall know every bush,
and I will trouble you young ladies, when each of you cut down your tree,
to spare a few. As for the view behind the house, I have seen nothing like
it. It is the same with North Wales; Snowdon, to my mind, looks much
higher and much more beautiful than any peak in the Cordilleras. So you
will say, with my benighted faculties, it is time to return, and so it is,
and I long to be with you. Whatever the trees are, I know what I shall
find all you. I am writing nonsense, so farewell. My most affectionate
love to all, and I pray forgiveness from my father.

Yours most affectionately,
CHARLES DARWIN.