APPENDIX A NOTES ON SPECIMENS COLLECTED IN THE CHILIAN BY MEMBERS OF MR. FITZ GERALD'S ANDES EXPEDITION BY PROFESSOR T. G. BONNEY, D.Sc., LL.D., F.R.S. (a) IN the description of these specimens it will be most natural and advantageous to commence with those collected at the greatest distance from the axis of the Andean Chain and at the lowest level. The first specimen (22) was obtained in the Horcones Valley, some distance east of Aconcagua; on the left bank of the river bearing the same name, to west-south-west of, and rather more than two and a half miles in a straight line from Mr. FitzGerald's base camp. It is a reddish limestone with part of the whorl of an ammonite. (b) 23, collected a little more than a mile farther up the valley, and on the opposite bank of this stream is a similar specimen. For description of these two, see Mr. Crick's Note on the Fossils (p. 333). (c) 12 (bis), comes from the same bank of the river, above three and a half miles farther up, and (9) from the slopes above on the same side. This bears the label "K2 Camp, loose (7th April, Gosse)." The specimen is about two inches in diameter, purplish or blackish in colour, apparently coated with iron-oxide, with a little of a whitish mineral and traces of malachite. It is not likely to repay a more intimate examination, being either a vein product or rock impregnated with metallic deposits. (d) 1. "K3 District, 12,000 feet, foot of mountain south of Aconcagua, large slabs appearing above sands and mud" nearly two miles beyond the last described (c), and on the left bank of the Horcones River. It is a piece, about a foot long, of Gypsum "marbled" with darkish lines, one face also being incrusted with a secondary deposit of the mineral of which the specimen is composed; it is stained a reddish colour. We come next to the specimens connected with the Torlosa Valley. Taking these in the order of lettering, we find on the left bank near the mouth of the valley (barely a mile from the last locality): (a) "Found loose (Vines)." A flattish triangular piece, not quite three inches in vertical height. Apparently a sedimentary rock consisting of a grey silty material, which effervesces moderately with hydrochloric acid, and is traversed by small veins of calc-spar; there is a reddish stain on the exterior. It was probably once a silt, possibly containing much volcanic dust. (b) "Stone found in springs north-east base of Torlosa (22nd April, Gosse)." A flattish specimen, with rounded edges about three inches in longest dimension, coated externally with an ochre-brown film, under which is a reddish-grey deposit; perhaps showing some indications of sulphur. These coatings conceal the actual material of the rock. The spring is probably chalybeate, and possibly may also contain sulphides or sulphates. It is added that the water was bad to drink, and the information is not surprising. (c) "Found just above water-line near springs, base of Torlosa; all the stones covered with the same white deposit." A rudely triangular piece, a little more than two inches in greatest length, of a rather hard compact grey rock, resembling a fine quartzose grit, but with some specks of felspar. The rock itself appears insensible to hydrochloric acid, but the white incrustation effervesces briskly. Without more minute examination (which would be wasting time) I cannot be quite certain of the nature of this rock, but it is not improbably an indurated volcanic dust. (d) "North-west side of dried-up spring (23rd April, Gosse)." Four specimens of calcite evidently deposited by water. All consist of two layers: one showing remnants of a third (at bottom). This seems to be a muddy limestone (the calcareous constituent being doubtless a precipitate). The next layer (about half an inch thick) has a rather cellular structure; over this is a slightly mammillated outer coating (about one-fifth of an inch thick) of calcite or aragonite in small crowded prisms. Both these layers are no doubt precipitates. A fifth specimen is a little lump of a yellowish-grey colour, about three-quarters of an inch in diameter, with some resemblance to the concretions called "race," in the brick earth of the Thames Valley. (e) "All the stones in water at mouth of spring like this (23rd April, Gosse)." A subangular stone, so thickly coated with rust that the rock itself is not visible. The water evidently is chalybeate; the stone is not likely to repay further examination. (f) See Mr. Crick's Notes, p. 335. (g) In springs, under water (25th April, Vines)." The specimen seems to be bounded by natural joint faces, which are covered with DESCRIPTION OF ROCK SPECIMENS 313 rust, the water being probably chalybeate. A cut surface discloses a compact dark rock with paler greyish spots. Microscopic examination shows a glassy base thickly crowded with lath-like microliths of plagioclase felspar, minute pyroxenes, ferrite and opacite. Scattered in this are larger grains of iron-oxide, some being hematite, and several, not so large, of a pale green mineral. Of this three types are noted; some irregular in shape, are aggregates of a fibrous mineral, in parts very dense, which has low polarisation tints, and resembles a serpentine. These are occasionally bordered with a thin layer of a clear mineral, and may occupy minute vesicles; others, more regular in form, show parallel cleavage planes. In the better preserved parts of these some exhibit straight extinction, others that of diallage, and slight differences in aspect may be noted. Hence I conclude that both diallage and a variety of enstatite have been present, and that the rock is a rather altered enstatite-andesite. A crack in it is filled with hematite. (h) See Mr. Crick's Notes, p. 335. (j) "South-east side, found below spring in quantities." Apparently a chip of a dark limestone or a calcareous mudstone, almost covered with a thin film of carbonate of lime. (k) "The north-west side of the valley in this rock (Vines)." Small fragments, of a purplish-grey rock, resembling a rather altered andesite. A green tint in some of the fragments suggests the presence of minute epidote; felspar can be distinguished; dark spots probably indicate pyroxene; some calcite is deposited on one side (a joint face); on the surface (probably similar) of a second chip is a group of small radiating crystals of a colourless transparent mineral, not effervescing with hydrochloric acid, and apparently rather too hard for a sulphate. Possibly it is a zeolite, but it seemed needless to carry the investigation further. (2) "Loose in bed of stream (17th April, Lightbody)." Four specimens of a rather platy or foliated selenite, showing the clinodiagonal cleavage faces. Apparently it has been formed in a yellowish-grey clay. (m) "Pure gypsum in quantities, mouth of valley, in debris and in sand." The label sufficiently describes the specimen, which evidently is a precipitate. (n) "Mouth of valley in quantities (22nd April, Vines)." A slab of darkish limestone (fairly brisk effervescence with hydrochloric acid). Weathered surfaces are a pale reddish grey, showing a subconchoidal fracture and a rather platy jointing; no signs of fossils. Not very unlike one of the darker Carboniferous limestones of England, but it might be of any age, from late Paleozoic to early Tertiary. Near to it occurs (19) “Shingle behind K3 (22nd April, Vines).” A small lump of gypsum, enclosing deep reddish-coloured bits,apparently of indurated mud. (On the right bank of the stream come in succession (m) with some more of ("), (ƒ), (1), (a), (†), (e), and then nearly on a line up the slope (g), (b), (c); on the left bank in the same order is (h and k), with (d) roughly opposite to (e)). 16. The next two specimens come from high up on the east side of the ridge bounding the Torlosa Valley on the west. "Whitish-yellow streak running east to west through brown rock (17), same colour throughout Torlosa." This is an elongated specimen (about three and a half inches in length), defined by irregular joint faces. It is of a pale pinkish-grey colour, with yellowish (felspathic) spots, and is of a redder tint on the exposed surfaces. On microscopic examination it appears doubtful whether any base remains; probably that is now devitrified: if not it is very thickly crowded with felspar microliths, some of which are more like sanidine than plagioclase. Both these minerals appear to occur among the larger crystals. All however are rather decomposed, numerous microliths of sericitic aspect being developed, which are often about one-tenth of an inch in diameter. There are grains of iron-oxide (? hematite), and several rudely outlined prisms-less than half the length of the felspar-consisting of a pale brown micaceous mineral, with opacite and ferrite. The cross-section of one or two suggests that these aggregates replace hornblende. A few small crystals of a nearly colourless mica are present, and two or three of apatite (?). The rock has been an andesite, probably with hornblende, possibly also with biotite. 17. A. This is a slab of fine-grained sandy mudstone of a rather dark reddish-brown colour. Under the microscope the rock is seen to be composed of small rather angular fragments of quartz and felspar, the latter being the more abundant, and some of them certainly plagioclase, with less angular fragments of felspathic lava, devitrified or crowded with microliths, not often scoriaceous. Cavities and the interstices of the ground-mass are occupied with a deep brown material, probably largely composed of iron-oxide. There are no signs of cleavage; the rock is probably an indurated stratified volcanic dust. 3. "K2 Camp. From solid rock; also lying in debris on Col, Buenavista Valley; seen also in many other places in Horcones Valley at 11,000 and 12,000 feet (7th April, Gosse)." Seven lumps of ore, the dominant material being a purplish-brown colour, inclining |