153

1834 June. (1) Port Famine

All the rocks in this district are of slate: 1790 it is generally compact, blueish black & but little fissile: Besides its cleavage, it is divided into parallel beds parallel to it. — These often alternate with grey calcareous varieties 1791; there are veins of quartz & calcareous spar. — In many places the slate contains much lime 1789, & in it these conta are imbedded curiously shaped concretions of dark aluminous limestone. —

They are very numerous; sometimes being cylindrical, globular, sausage-shaped & radiated: — I found a few of these lumps impressed with the shape of some oth animal. — They somewhat, resemble a cornu-ammonis, but not coiled up, only in the form of a siphon 1785 ... 1788; — one of the largest, measured following the centre of curvature, was 21 inches: from extremity to extremity, out of which the short leg was 7. inches: the breadth 2.7 inch. — There was another organic remain (1813) 1813. — At Rocky Point, in the slate 1812, there is a green conglomerate or a breccia greywacke - [malanorum] fissure of [stratum]; it was included in a sort of vein like masses & passed insensibly into the slate 1811; there it was difficult to say, whether it formed a parallel cleavage layer with the slate or true stratum. 2059 ... 2965 — It contained some bivalve shells & traces of spiral univalves. — In Bougainville Voyage. C. Remarkable (some miles to the South) is said to be composed of conglomerate. —

I saw the slate traversed by a few narrow dykes of earthy, fusible greenstone (?), their course was torturing 1792; some slate included between two neighbouring veins was not in the least altered. — One of the dykes, thinned out & ended in nothing. —

strike out reference & Port Desire

It may be doubted whether this is true volcanic greenstone.

153v [blank]

154

1834 June. (2) P. Famine

M. Tarn is situated 7 miles to the S of Port Famine it is 2600 ft high (a); only at the summit any base rock is seen; it is essentially a coarse, rubbly, compact slate generally blueish, sometimes yellowish 1810; the parting of the seams ferruginous:

the structure is curious, appearing like so many immense balls 3 or 4 feet in diameter, round which the laminae of slate old; this is chiefly shown by its decomposition. Some of the rocks contains pyrites & much iron. —

I found near the summit, a univalve, (& bivalve which I lost) bones of an Echinus?: & numerous fragments of impressions of a special Nautilus. 1801 ... 1809 — I saw near Port Famine, an impression of one of these shells, twice as large t as the specimens. — The cleavage or stratification was very obscure; the highest point dipped to the SW 1/2 S ∠ 2 NE by 1/2 N ∠ 28;

strata
the most usual direction of strata varied from this to NW by N & SE by S. — & this appeared to be the prevailing direction of the intricate mass of hills. — At Port Famine. I have said the laminae of slate, & beds of varying mineralogical nature are parallel. — The most usual strike is perhaps NW by 1/2 W &c; the forms of the creeks & promontories is NW & SE. B — At M. Tarn the dip is northern. — by looking at the diagram the order of dips will at once be seen —; the angle varies from vertical to very small. — At Rocky Point all the dips are southern, we then have to the North small inclined beds dipping northerly, & then inclined in same direction but at a higher angle.

[text in margin largely too faint and illegible]

154 verso

(a) I noticed here, & in other parts of T. del F. that wherever snow lies during the greater part of the year the rock is much decomposed, & converted into earth & small fragments. —

(B) But the coast & line & deep arm of the sea runs N & S. — But it may be observed this arm is not parallel to the greater number of channels. —

154A

[sketch] [map]
(N) m Rocky P
xx
M.St. Phillip 1308
8 mile
Sxx D F (b) a
St Anna P.
a a a
P. Famine

strike

(a). N 48. W — ∠ 56 southerly

(b) N. 55. W — ┴° or nearly to S slightly tortuous

(c) N. 45. W ∠ 25. S

(D) N. 47. W. ∠ 22. S

(E) N. 32. W ∠ 38 S

(F) irregular, no decided strata

(G) dip to NE ∠ 5° or horizontal

(H) N. 58. W ∠ 11° northerly

(K) N. 52 W ∠ 17. N

(L) N. 47. W ∠ 11. N

(M) N. 47 W ∠ 45. N

(N) N 42 W. ∠ ┴° or N. —

[sketch] [map pasted in]

Rocky P.
M. Philip 1308
St. Anna P.
Port Famine
[Bridge]
M. Tarn 2600
C. Remarquable
C. [Frowassi]

155

1834 June. (3) P. Famine

It hence forms a sort of anticlinal band. — It is curious this should occur at the very place, where the slate ranges begin to be much lowered. — The sea however, close in shore is very. 3 to 400 feet. — The parallelism of the cleavage or stratification. (for I am quite at a loss. which to call it) is at once evident with the West part of St^s of Magellan &c &c.

Magdalen Channel

range cove at Cape Tarn, I found a greenish slate, with a distinct cleavage which dipped at about 45° to S: the slate is very hard, compact, & slightly crystalline, & containing specks of iron pyrites 2074 2075: it evidently had suffered considerable alteration from its original nature. — Two or three hundred yards from this I found the same slate in contact & traversed by dykes connected with the mass of greenstone which formed the main part of a neighbouring high hill. — The diagram shows the form of junction.

[sketch] Greenstone b A slate

The greenstone is highly crystalline: containing composed of hornblende & feldspar: 2079 it contains mica & pyrites & is traversed by veins of quartz: on the large scale has a tending to columnar structure, & the sides of the hills composed of it. are very steep. —

Specimens (2076 & 2077) are taken from part A: & shows the actual contact: the slate is very different from the its usual laminated soft nature, & is here pale colored & highly crystalline:

Where the sea had worn a smooth surface at (B)

155 verso

(a) Re vein of quartz, several inches broard traversed slate & greenstone

R.N. p. 7 quartz in dikes

156

1834 June. 4 Port Famine (170)

Magdalen Channel

angular fragments of slate might be most clearly seen in the greenstone: in a hand specimen the edges blended together: the fragments only differed from the surrounding mass, by having the hornblende more abundant & more finely gra crystalline & in containing a few, large crystalls of feldspar. — 2078 Specimen (2078) is part of one of these (but a very bad specimen) the white corner is the surrounding rock: the slate here is not sufficiently porphyritic to represent the general appearance. — it is curious to see (B) so very much altered & A not, although quite surrounded. — Were the fragments (B) brought from below? — The greenstone resembles in appearance the rock of the SW arm of the Beagle Channel & that found in the midst of the singular rocks of Hardy Peninsula: I was much pleased to see it here cutting & overlying & altering the slate. — From general appearance I have no doubt that all the West side of Magdalen Channel is of this greenstone; the higher hills, with jagged points here, (& between this & the Barbara Channel) are of altered slates. M. Sarmiento on its West side comes down in one steep slope to the waters edge.

Warp Cove is in the very WNW line & then we have a South dip. — there seems no continuation of that lofty range through Clarence island. — On passing out by the Cockburn Channel, the hills or islands are on each side, much lower, more very rounded & very barren (a): the rocks look like granite

156 verso

(a) I believe this is the general character of the outer coast. — When looking at their weather-beaten faces, it appeared to me certain that, once, formerly they had been exposed for a long period the fury of the western ocean, in the manner as the numerous low rocks & reefs, are now incessantly beaten by the present Pacific. I feel little doubt, that the rounded granite & greenstone hills, are only the basal parts of former lofty mountains composed of softer materials. — Will not this explain. the general fringe of such rock on the outer crusts, both here, in Scotland, & in Norway? — — The channels are very deep; hence the is this owing to the granite being protruded into slate in paps & ridges (or slate melted into such forms) or to great fractures during the upheaval.

Both conjectures have their difficulties. If the former, how has the intermediate slate been removed, if the latter, how comes the cleavage is so regular. —

(b) The Sarmiento range is the main one of the WNW cleavage district. —

NB. May there in truth have been a depressing period in T. del Fuego? —