Coquimbo Region, Chile: Historical records

 Literatura: Charles Darwin

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Texto Charles Darwin: Coquimbo
chap. IX. Gravel-Terraces of Coquimbo. p.252-254

Valley of Coquimbo. — The narrow coast-plain sends, as before stated, an arm, or more correctly a fringe on both sides, but chiefly on the southern side, several miles up the valley. These fringes are worn into steps or terraces, which present a most remarkable appear­ance, and have been compared (though not very cor­rectly) by Capt. Basil Hall, to the parallel roads of Glen Roy in Scotland : their origin has been ably discussed by Mr. Lyell.1 The first section which I will give, is not drawn across the valley, but in an east and west line at its mouth, where the step-formed terraces de­bouch and present their very gently inclined surfaces towards the Pacific.

The bottom plain (A) is about a mile in width, and rises quite insensibly from the beach to a height of twenty-five feet at the foot of the next plain: it is sandy, and abundantly strewed with shells.

Plain or terrace (B) is of small extent, and is almost concealed by the houses of the town, as is likewise the escarpment of terrace (C).
On both sides of a ravine, two miles- south of the town, there are two little ter­races, one above the other, evidently corresponding with (B) and (C); and on them marine remains of the species already enumerated were plentiful. Terrace (E) is very narrow, but quite distinct and level; a little southward of the town there were traces of a -terrace (D) inter­mediate between (E) and (C). Terrace (F) is part of the fringe-like plain, which stretches for the eleven miles along the coast; it is here composed of shingle, and is 100 feet higher than where composed of calcareous matter. This greater height is obviously due to the quantity of shingle, which at some former period has been brought down the great valley of Coquimbo.

Considering the many shells strewed over the terraces (A) (B) and (C), and a few miles southward on the calcareous plain, which is continuously united with the upper step-like plain (F), there cannot, I apprehend, be any doubt, that these six terraces have been formed by the action of the sea; and that their five escarp­ments mark so many periods of comparative rest in the elevatory movement, during which the sea wore into the land. The elevation between these periods may have been sudden and on an, average not more than seventy-two feet each time, or it may have been gradual and insensibly slow. From the shells on the three lower terraces, and on the upper one, and I may add on the three gravel-capped terraces at Conchalee, being all littoral and sub-littoral species, and from the analogical facts given at Valparaiso, and lastly from the evidence of a slow rising lately or still in progress here, it appears to me far more probable, that the movement has been slow. The existence of these successive escarpments, or old clifflines, is in another respect highly instructive, for they show periods of comparative rest in the elevatory movement, and of denudation, which would never even have been suspected from a close examination of many miles of coast southward of Coquimbo.
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