Gives details of his observations which lend support to the view that Chile is rising with respect to the sea. Reports some observations and opinions with regard to earthquakes and volcanic action in the area.
By the arrival of the Beagle on the 14
A few days ago I went along the Coast from Playa-ancha towards Laguna, and in a ravine nearly parallel with that of Quebrada Verde and about 300 yards from the sea, I observed that it had intersected several strata of shells leaving them exposed to the right and left on both sides of the ravine, on one side they continued up a series of steps or beaches forming a little hill about 80 feet high from the brink of the ravine, and about 350 feet above the level of the sea—
The face of the hill was much covered with brush-wood, so that it was only by pulling
it up and removing the earth that the shells could be found, and the steps were not well
defined— The bottom of the ravine and the loose stones in it were gneiss of a
very compact character with veins of feltspar; on digging a hole into one of the sides
of the ravine about 3 feet from the edge I found the pelvis of some quadruped
in a state of great decay. it was too small for a horse. I br
The situation is almost inaccessible from the sea, therefore it is not likely that they have been conveyed there for the purposes of food, nor in after times by the Spaniards to make lime as they would not have placed them round the sides of a hill—
I ought to mention, that the shells higher up were much more decayed than those lower down, so if a rising has taken place, it has been per gradus & not per saltum—
I do not know whether you have examined the sea cliffs towards Viņa de la Mar a little beyond the village of the Baron where you would observe the rocks about 14 feet above high water with numerous funnel shaped perforations, caused no doubt by lithophagi, & on a pointed rock which can only be reached by climbing with the hands & feet some balani are adhering to the surface on removing the dung of the gulls with which it is entirely covered— At the same level where you find the funnel shaped perforations, and where the rock is much decomposed, the Cactus tuna & other plants which require little soil and moisture are growing most luxuriantly a sign that they are always above high water mark— You will tell me that the sea may have retired as it has done in the Almendral from the detritus of the surrounding hills, but the bottom is all rocky and the water deep close to the shore, as I have frequently bathed there I am well able to judge— I am very possibly describing a spot which you have observed with more enquiring eyes than mine as I think you mentioned you had been round the rocks under the Castle of the Baron. if so, I am glad of it—
You are possibly aware that there is a general opinion amongst the natives that the sea is fallen from the great difference which has taken place in the depth of the Bay in the last 50 years, and when you wish to gain any information from them on that point, you must give in to that opinion, or they will think you mad if you ask them whether the earth is rising—
As at present we have no data to go by, it is difficult to know whether there are paroxysmal risings or a chronic impulsion however in Central America a high chain of hills were thrown up in the course of four years from 1824 to 1828, and a town which was in a plain became surrounded on one side by high hills—
The piece of fossil wood you allude to, and which I send was found in a ravine beyond Playa-ancha towards Quebrada verde, but I did not find it in situ, but in the water amongst the rocks. the sides of the ravine were a sandy conglomerate with rounded pieces of indurated clay similar to those in the road of the Alto del Puerto. the bottom of the ravine appeared a sort of grünsteinic rock—
You ask me what is my opinion respecting the direction of sounds accompanying earthquakes, from my own observation I have thought that it comes in the direction of the line of movement, but I am far from being certain that the opinion is correct, as some people have thought that the sound was in one direction & I thought in the opposite—
The shocks generally proceed from the North, and the great earthquake which happened here in Nov. 1822 came from that quarter, and the sea flowed in as ``black as ink and the anchors & chains of ships anchored to windward shook dreadfully before they felt the shock.'' I merely mention this as having heard it from those who were here at the time without answering for the the truth of it, but I believe there is no doubt of the water coming in quite black from the North;— the Barometer in our store is a bent tube 49 Inches long, 19 of which is the utmost range, sunk down below the graduated part, equal to 20 Inches English previous to the earthquake of 1822—and whatever the season of the year may be rain almost always follows a heavy earthquake. the one in Nov 1822 was followed by torrents of rain— The natives say that when the volcanoes are active, there is no danger of earthquakes, but when they are quiet for a long period heavy shocks may be expected—after an earthquake they generally commence burning again— The people of the Country have various signs of a shock, such as the stars twinkling, rats making a noise, but there is not the slightest truth in it. Whenever the noise preceding a shock takes place all animals appear to be alarmed, the horse starts & snorts the fowls cackle & the dogs bark—
I wish much to hear of your report respecting the islands in the Pacific, and it will be curious if you find a sinking of the land there, & a rising here—
I sincerely hope we may yet meet in the olden World and at all times it will give me
much pleasure to hear from you and with every wish for your health & welfare | I
remain | Dear Darwin | Yours sincerely | Rob
- f1 277.f1CD used information from this letter in his paper for the Geological Society of 4 January 1837 (Collected papers 1: 41--3) and in South America, pp. 31--5. Also included are data supplied by Alison in a memorandum on changes of land level from 1640 to 1834 (from R. E. Alison, [June? 1834]).
- f2 277.f2One of the explanations advanced at the time for the existence of shells above sea level was that they were the remains of shellfish used for food at sites of earlier habitations. CD was especially cautious in his observation of shell deposits because he had recently seen heaps accumulated by the natives of Tierra del Fuego (see `Observations of proofs of recent elevation on the coast of Chili', Collected papers 1: 41--3, and letter to [Alexander Burns Usborne], [c. 1--5 September 1835]). The correct names for Alison's shells are Concholepas, Patellae, and Mytilus. See South America, p. 32.
- f3 277.f3CD had apparently discussed with Alison his hypothesis that a subsidence of land had taken place in the Pacific concomitant with the elevation of the South American continent.