Robert Fitzroy - Narrative of the surveying voyages of His Majesty's ships Adventure and Beagle, between the years 1826 and 1836

Our road hence was rather more varied: always steep, but sometimes free from impediment. Here and there we observed the boggy soil was faced with a small plant ( Chamitis sp. ) of a harsh character, growing so thick and close as to form large tufts, over which we walked as on hard ground. We struggled through several thickets of stunted beech-trees, with a thick jungle of Berberis underneath, whose strong and sharp thorns penetrated our clothes at every step; and began to find the fatigue very oppressive: some of my boat's crew suffered much, being unused to such exercise. At last we approached the place where Mr. Cooke and his party had established themselves, and upon hailing, were invigorated by a cheer in reply. We reached the bivouac in a very way-worn condition, and found, to our great comfort, the tent pitched, and a good fire burning. 42 42 The height of this place, as shown by the barometer, on the ascent, was 941 feet, and, on the descent, 973 feet.

The ground was so exceedingly wet, that although we slept upon branches, forming a layer at least a foot thick, we found ourselves, in the night, lying as if in a morass, and suffering from cold, even with a large fire blazing at our feet. At daylight next morning, just as we were starting, a boat was seen sailing round Cape San Isidro, which, by the aid of a telescope, I made out to be the Hope.

We resumed the ascent, and passed over, rather than through, thickets of the crumply-leaved beech, which, from their exposure to the prevailing winds, rose no higher than twelve or fourteen inches from the ground, with widely-spreading branches, so closely interwoven, as to form a platform that bore our weight in walking. We next traversed an extent of table-land, 43 43 On this table-land the barometer stood at 27,767. Temperature of the air 46°,5, and of the mercury 47°,5, which gave the elevation 1,327 feet. much intersected by ponds of water. Mr. Tarn shot two plovers of a new species ( Charadrius rubecola , Zool. Jour. vol. iv. p. 96), and a snipe. We then ascended three or four hundred feet, and crossed a deep ravine. The bottom of the ravine was clay-slate in a decomposing state, but the surface of the ground was strewed with pebbles of granite. Another plain, with many ponds, succeeded; the intervening spaces being covered with tufts of chamitis, and studded here and there with small clusters of dwarf beech; but the ground was so hard, and firm, that we proceeded rapidly, without fatigue, until we attained the height of 1,800 feet, when the ascent became very steep. Near the summit lay a large mass of snow, rapidly melting away. We reached the highest pinnacle of the mount at seven o'clock (having left our resting-place at four), and immediately set up the instruments. I was obliged to avail myself of Mr. Tarn's assistance to hold the barometer, whilst two of my boat's crew held the legs of the theodolite-stand, for the wind was blowing very strongly, and the edge of a precipice was close to us, perpendicular for many hundred feet, and thence downwards so steep, that any body going over would fall at least a thousand feet. The theodolite-stand was unavoidably placed within a very few inches of the edge, and I took a round of angles, suffering, however, intense pain from the piercing coldness of the wind, which, heated as we were by the ascent, was much felt, though the temperature was not lower than 39°. I was lightly clothed, and should have fared badly, had not one of the party lent me his Flushing jacket, while he descended under the lee of the mountain-top to make a fire. The barometer stood at 26,618, the temperature of the air being 40°, and of the mercury 43°. 44 44 The result of the barometric observation for the height of Mount Tarn is as follows: By angular measurement from Observation Cove, Port Famine, with theodolite, allowing 1⁄12 of the intercepted arc for terrestrial refraction, the height is 2,850 feet. Another observation, with the sextant, made it 2,855 feet. The mean 2,852 I consider more correct, from the difficulty of obtaining a correct reading of the barometer on the summit. Unfortunately the day was very cloudy, and many squalls of sleet and rain, which obscured the hills, passed whilst I was taking bearings. To the N.E., towards the supposed Sebastian Channel, the horizon was too hazy to allow much view. A deep inlet was seen in that direction; but whether the land closed round, or whether a channel was at the bottom, we could not distinguish. A considerable body of water was observed to the southward of Cape St. Valentyn, behind Lomas Bay, but its extent was screened from our view by the intervention of the Lomas hills. It appeared to be a channel, the opposite or eastern side of it being formed by the high ranges previously seen from Point St. Mary. Cordova's Ports San Antonio and Valdez were distinctly made out; but, to the southward, every thing was enveloped in mist.

The bearings and observations, which occupied me nearly two hours, being completed, we all adjourned to a sheltered cleft in the rock close to our station, where we soon recovered the use of our fingers. 45 45 By Daniell's hygrometer, used in this sheltered spot, I found the temperature of the air to be 48°; dew point 41°: but upon exposing the instrument to the wind, the air was 39½°, and the dew point 36°: the difference in the former being 7°; and the latter 3½°; from which the following results are obtained: The above being the difference in the short space of three feet apart; the instrument, in the first case, being just under the lee of the rocky summit of the mountain, and in the last, above it, exposed to the wind.

Having accomplished our object, we began the descent. In a comparatively mild and agreeable spot, I again set up the theodolite and barometer, while some of the party employed themselves in fruitless attempts to kindle a fire. The height, by the barometer, proved to be 1,845 feet above the sea; and the bearings from this station were much better than those I had taken from the exposed summit.

We reached our tent at noon, having been absent seven hours. At three we reached the beach, where the barometer stood at 29,312 (air 61.°3, 46 46 The air was so dry this afternoon that I failed to procure a deposit of dew upon Daniell's hygrometer, although the internal temperature was lowered from 61° to 37°. One of Jones's portable hygrometers was also tried, and the temperature was lowered to 31°½ without a deposit; so that, the difference being more than thirty degrees, the expansive force of the air must have been less than 212, the dryness, on the thermometric scale, less than 367, and the weight of vapour, in a cubic foot of air, less than 2,355 grains. and mercury 62,°5).

Excepting near the sea, where clay-slate (very similar to that of Point St. Anna, but with an opposite dip) showed itself, the side of the hill is clothed with trees and underwood, and no rock is visible until one arrives at the ravine. Around the summit of Mount Tarn the ground is bare, but so covered with small decomposed fragments, that the solid rock only appears occasionally: it is very hard, and breaks with a conchoidal fracture: some of the specimens which we detached bore indistinct impressions of organic remains. We also found, projecting from the rock in which they were embedded, nodules, or small rounded masses of stone, in an advanced state of decomposition, mouldering away in laminar forms somewhat resembling the inner leaves of a cabbage. Several were brought away carefully, but before we arrived on board they had crumbled to pieces: the nucleus was quite hard, but was surrounded by concentric laminæ, more brittle the nearer they approached to the outer surface. It seemed as if the face of the summit above-mentioned was covered with the decomposing fragments of these nodules.