CONCEPCION.
Sailing northward from Valdivia, the coast-cliffs are seen, first to assume near the R. Tolten, and thence for 150 miles northward, to be continued with the same mineralogical characters, immediately to be described at Concepcion. I heard in many places of beds of lignite, some of it fine and glossy, and likewise of silicified wood; near the Tolten the cliffs are low, but they soon rise in height; and the horizontal strata are prolonged, with a nearly level surface, until coming to a more lofty tract between points Rumena and Lavapie. Here the beds have been broken up by at least eight or nine parallel lines of elevation, ranging E. or E.N.E. and W. or W.S.W. These lines can be followed with the eye many miles into the interior; they are all uniclinal, the strata in each dipping to a point between S. and S.S.E. with an inclination in the central lines of about forty degrees, and in the outer ones of under twenty degrees. This band of symmetrically troubled country is about eight miles in width.
The island of Quiriquina, in the Bay of Concepcion, is formed of various soft and often ferruginous sandstones, with bands of pebbles, and with the lower strata sometimes passing into a conglomerate resting on the underlying metamorphic schists. These beds include subordinate layers of greenish impure clay, soft micaceous and calcareous sandstones, and reddish friable earthy matter with white specks like decomposed crystals of feldspar; they include, also, hard concretions, fragments of shells, lignite, and silicified wood. In the upper part they pass into white, soft sediments and brecciolas, very like those described at Chiloe; as indeed is the whole formation. At Lirguen and other places on the eastern side of the bay, there are good sections of the lower sandstones, which are generally ferruginous, but which vary in character, and even pass into an argillaceous nature; they contain hard concretions, fragments of lignite, silicified wood, and pebbles (of the same rocks with the pebbles in the sandstones of Quiriquina), and they alternate with numerous, often very thin layers of imperfect coal, generally of little specific gravity. The main bed here is three feet thick; and only the coal of this one bed has a glossy fracture. Another irregular, curvilinear bed of brown, compact lignite, is remarkable for being included in a mass of coarse gravel. These imperfect coals, when placed in a heap, ignite spontaneously. The cliffs on this side of the bay, as well as on the island of Quiriquina, are capped with red friable earth, which, as stated in the Second Chapter, is of recent formation. The stratification in this neighbourhood is generally horizontal; but near Lirguen the beds dip N.W. at an angle of 23 degrees; near Concepcion they are also inclined: at the northern end of Quiriquina they have been tilted at an angle of 30 degrees, and at the southern end at angles varying from 15 degrees to 40 degrees: these dislocations must have taken place under the sea.
A collection of shells, from the island of Quiriquina, has been described by M. d’Orbigny: they are all extinct, and from their generic character, M. d’Orbigny inferred that they were of tertiary origin: they consist of:—
1. Scalaria Chilensis, d’Orbigny, “Voyage, Part Pal.” 2. Natica Araucana, d’Orbigny, “Voyage, Part Pal.” 3. Natica australis, d’Orbigny, “Voyage, Part Pal.” 4. Fusus difficilis, d’Orbigny, “Voyage, Part Pal.” 5. Pyrula longirostra, d’Orbigny, “Voyage, Part Pal.” 6. Pleurotoma Araucana, d’Orbigny, “Voyage, Part Pal.” 7. Cardium auca, d’Orbigny, “Voyage, Part Pal.” 8. Cardium acuticostatum, d’Orbigny, “Voyage, Part Pal.” 9. Venus auca, d’Orbigny, “Voyage, Part Pal.” 10. Mactra cecileana, d’Orbigny, “Voyage, Part Pal.” 11. Mactra Araucana, d’Orbigny, “Voyage, Part Pal.” 12. Arca Araucana, d’Orbigny, “Voyage, Part Pal.” 13. Nucula Largillierti, d’Orbigny, “Voyage, Part Pal.” 14. Trigonia Hanetiana, d’Orbigny, “Voyage, Part Pal.”
During a second visit of the “Beagle” to Concepcion, Mr. Kent collected for me some silicified wood and shells out of the concretions in the sandstone from Tome, situated a short distance north of Lirguen. They consist of:—
1. Natica australis, d’Orbigny, “Voyage, Part Pal.” 2. Mactra Araucana, d’Orbigny, “Voyage, Part Pal.” 3. Trigonia Hanetiana, d’Orbigny, “Voyage, Part Pal.” 4. Pecten, fragments of, probably two species, but too imperfect for description. 5. Baculites vagina, E. Forbes. 6. Nautilus d’Orbignyanus, E. Forbes.
Besides these shells, Captain Belcher found here an Ammonite, nearly three feet in diameter, and so heavy that he could not bring it away; fragments are deposited at Haslar Hospital: he also found the silicified vertebrae of some very large animal. (“Zoology of Captain Beechey’s Voyage” page 163.) From the identity in mineralogical nature of the rocks, and from Captain Belcher’s minute description of the coast between Lirguen and Tome, the fossiliferous concretions at this latter place certainly belong to the same formation with the beds examined by myself at Lirguen; and these again are undoubtedly the same with the strata of Quiriquina; moreover; the three first of the shells from Tome, though associated in the same concretions with the Baculite, are identical with the species from Quiriquina. Hence all the sandstone and lignitiferous beds in this neighbourhood certainly belong to the same formation. Although the generic character of the Quiriquina fossils naturally led M. d’Orbigny to conceive that they were of tertiary origin, yet as we now find them associated with the Baculites vagina and with an Ammonite, we must, in the opinion of M. d’Orbigny, and if we are guided by the analogy of the northern hemisphere, rank them in the Cretaceous system. Moreover, the Baculites vagina, which is in a tolerable state of preservation, appears to Professor E. Forbes certainly to be identical with a species, so named by him, from Pondicherry in India; where it is associated with numerous decidedly cretaceous species, which approach most nearly to Lower Greensand or Neocomian forms: this fact, considering the vast distance between Chile and India, is truly surprising. Again, the Nautilus d’Orbignyanus, as far as its imperfect state allows of comparison, resembles, as I am informed by Professor Forbes, both in its general form and in that of its chambers, two species from the Upper Greensand. It may be added that every one of the above-named genera from Quiriquina, which have an apparently tertiary character, are found in the Pondicherry strata. There are, however, some difficulties on this view of the formations at Concepcion being cretaceous, which I shall afterwards allude to; and I will here only state that the Cardium auca is found also at Coquimbo, the beds at which place, there can be no doubt, are tertiary.
NAVIDAD. (I was guided to this locality by the Report on M. Gay’s “Geological Researches” in the “Annales des Scienc. Nat.” 1st series tome 28.)
The Concepcion formation extends some distance northward, but how far I know not; for the next point at which I landed was at Navidad, 160 miles north of Concepcion, and 60 miles south of Valparaiso. The cliffs here are about eight hundred feet in height: they consist, wherever I could examine them, of fine-grained, yellowish, earthy sandstones, with ferruginous veins, and with concretions of hard calcareous sandstone. In one part, there were many pebbles of the common metamorphic porphyries of the Cordillera: and near the base of the cliff, I observed a single rounded boulder of greenstone, nearly a yard in diameter. I traced this sandstone formation beneath the superficial covering of gravel, for some distance inland: the strata are slightly inclined from the sea towards the Cordillera, which apparently has been caused by their having been accumulated against or round outlying masses of granite, of which some points project near the coast. The sandstone contains fragments of wood, either in the state of lignite or partially silicified, sharks’ teeth, and shells in great abundance, both high up and low down the sea-cliffs. Pectunculus and Oliva were most numerous in individuals, and next to them Turritella and Fusus. I collected in a short time, though suffering from illness, the following thirty-one species, all of which are extinct, and several of the genera do not now range (as we shall hereafter show) nearly so far south:—
1. Gastridium cepa, G.B. Sowerby. 2. Monoceros, fragments of, considered by M. d’Orbigny as a new species. 3. Voluta alta, G.B. Sowerby (considered by M. d’Orbigny as distinct from the V. alta of Santa Cruz). 4. Voluta triplicata, G.B. Sowerby. 5. Oliva dimidiata, G.B. Sowerby. 6. Pleurotoma discors, G.B. Sowerby. 7. Pleurotoma turbinelloides, G.B. Sowerby. 8. Fusus subreflexus, G.B. Sowerby. 9. Fusus pyruliformis, G.B. Sowerby. 10. Fusus, allied to F. regularis (considered by M. d’Orbigny as a distinct species). 11. Turritella suturalis, G.B. Sowerby. 12. Turritella Patagonica, G.B. Sowerby (fragments of). 13. Trochus laevis, G.B. Sowerby. 14. Trochus collaris, G.B. Sowerby (considered by M. d’Orbigny as the young of the T. laevis). 15. Cassis monilifer, G.B. Sowerby. 16. Pyrula distans, G.B. Sowerby. 17. Triton verruculosus, G.B. Sowerby. 18. Sigaretus subglobosus, G.B. Sowerby. 19. Natica solida, G.B. Sowerby. (It is doubtful whether the Natica solida of S. Cruz is the same species with this.) 20. Terebra undulifera, G.B. Sowerby. 21. Terebra costellata, G.B. Sowerby. 22. Bulla (fragments of). 23. Dentalium giganteum, do. 24. Dentalium sulcosum, do. 25. Corbis (?) laevigata, do. 26. Cardium multiradiatum, do. 27. Venus meridionalis, do. 28. Pectunculus dispar, (?) Desh. (considered by M. d’Orbigny as a distinct species). 29, 30. Cytheraea and Mactra, fragments of (considered by M. d’Orbigny as new species). 31. Pecten, fragments of.