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1834 Feb Tierra del Fuego Appendix (79)

Wollaston Is^d

I add these notes made during this visit, at to those of P79. because the rocks seem to have most connection. — In neither case do I understand their nature. — The present situation is about 10 miles to the SE of Sunday bay. — The commonest rock is a blackish green 1866 & 1867. very little crystalline amphibolic one & which seems to partake in many of the characters of slate. — Externally however it is divided on a larger scale by numerous. smooth planes of divisions. — Another common variety is the same rock. appearing to contain fragments of slate (as in Feldspathic rock in Navarin Is^d). — The surface, produced by weathering 1868 produces the resemblance of a breccia in a very strong degree. — At the foot of a hill which will be described. there is rock similar (1866.) also one occurring with red crystals (1869) 1869, in which a Greenstone occurs in globular concretions 1870. it contains pyrites; & merely forms a mass in the other rocks. — Ascending one of the loftiest of the rugged hills, we have at the base rock like (1866) divided by numerous planes of into great shoals. — the most abundant plane dipped at ∠ 18° to S 1/2 E. — We There is also much of the Breccia — like rock; In the higher parts this becomes less frequent; there is however a variegated pale yellowish feldspathic rock 1854 penetrated & blending with what resembles a blank slate? On the rough broken ridge, a fine grained, more

97A

[printed map:]

Chart of a Part of South America.

Surveyed by order of
the R^t. Hon^ble the Lords Commissioners
of the Admiralty under the Direction of Cap^t. P.P. King R.N.
During the Years 1826-30.

Purple

Purple] added in pencil in Darwin's hand. There appear to be traces of watercolour added to the coast near Port Desire.

97

(79

1834 Feb T. del Fuego

Wollaston Is^d

crystalline amphibolic rock (1853) 1853 1855. it occurs with variegated sort & with globular connection of a black, sonorous fine-grained amphibolic rock with a conchoidal fracture. — These three rocks are traversed by irregular vein like masses composed of several minerals 1859 ... 1865, of which garnets are the most abundant. & some of which appear curious. — The very peaks are chiefly composed of a porphyry. 1856 1857 of amphibolic rock with white opake feldspar crystals, with this is the variety (1853). — In these rocks there were some small quartz veins! —

The porphyry is traversed (a) by vertical smooth planes which run in N 27° W & S 27° E line & in which there are low crests. — The chief ridges however run in a W 3° N & E 3° S. line; thus intersecting each other at an angle of 60°. — strata obscure cleavage place of colsum & harshness

But this cannot be of general occurrence, for the island is composed of the most rough & jagged peaks, which are very steep, & in the circular valleys there are lakes. — Are these more crystalline peaks the lower rocks (1866 ... 68) altered by heat & are not these latter, also transfigured slate?? The feldspathic rocks in Sunday Bay is accompanied by slate. —

I may here mention, that with respect to the conglomerate P90 found in this Island, containing red scoriae &c &c if as perhaps it probably it should be pronounced to be volcanic. yet it must owe its origin be of from to very ancient one, V oth. side

strata…hardeness] added pencil.

97 verso

volcano, one in which the regular cone, crater & streams of lava have been worn away. — I think this. because I have now seen all the East side & formerly very nearly all of the West & Southern parts & amongst such strongly marked peaks a volcano could not fail to be seen. —

(a) In the Porphyry there were also planes of alteration of color & hardness & division which dipped at small angle to the S.