with Madrid), grapes and figs ripen, but are not common; olives seldom ripen even partially, and oranges not at all. These fruits, in corresponding latitudes in Europe, are well known to succeed to perfection; and even in this continent, at the Rio Negro, under nearly the same parallel with Valdivia, sweet potatoes (convolvulus) are cultivated; and grapes, figs, olives, oranges, water and musk melons, produce abundant fruit. Although the humid and equable climate of Chiloe, and of the coast northward and southward of it, is so unfavourable to our fruits, yet the native forests, from lat. 450 to 380, almost rival in luxuriance those of the glowing intertropical regions. Stately trees of many kinds, with smooth and highly-coloured barks, are loaded by parasitical monocotyledonous plants; large and elegant ferns are numerous, and arborescent grasses entwine the trees into one entangled mass to the height of thirty or forty feet above the ground. Palm-trees grow in lat. 37°; an arborescent grass, very like a bamboo, in 40°; and another closely allied kind, of great length, but not erect, flourishes even as far south as 450.

An equable climate, evidently due to the large area of sea compared with the land, seems to extend over the greater part of the southern hemisphere; and as a consequence, the vegetation partakes of a semi-tropical character. Tree-ferns thrive luxuriantly in Van Diemen's Land (lat. 45°), and I measured one trunk no less than six feet in circumference. An arborescent fern was found by Forster in New-Zealand in 46°, where orchideous plants are parasitical on the trees. In the Auckland Islands, ferns, according to Dr. Dieffenbach,* have trunks so thick and high that they may be

* See the German translation of this Journal; and for the other facts, Mr. Brown's Appendix to Flinders's Voyage.

HEIGHT OF THE SNOW-LINE.

315

almost called tree-ferns; and in these islands, and even as far south as lat. 55° in the Macquarrie Islands, parrots abound.

On the Height of the Snow-line, and on the Descent of the Glaciers, in South America. For the detailed authorities for the following table I must refer to the former edition :

As the height of the plane of perpetual snow seems chiefly to be determined by the extreme heat of the summer rather than by the mean temperature of the year, we ought not to be surprised at its descent in the Strait of Magellan, where the summer is so cool, to only 3500 or 4000 feet above the level of the sea; although in Norway we must travel to between lat. 670 and 700 N., that is, about 140 nearer the pole, to meet with perpetual snow at this low level. The difference in height, namely, about 9000 feet, between the snow-line on the Cordillera behind Chiloe (with its highest points ranging from only 5600 to 7500 feet) and in central Chile (a distance of only 9° of latitude), is truly wonderful. The land from the southward of Chiloe to near Concepcion (lat. 37°), is hidden by one dense forest dripping with moisture. The sky is cloudy, and we have seen how badly the fruits of Southern Europe succeed. In central Chile, on the other hand, a little northward of Concepcion,

On the Cordillera of central Chile, I believe the snow-line varies exceedingly in height in different summers. I was assured that during one very dry and long summer all the snow disappeared from Aconcagua, although it attains the prodigious height of 23,000 feet. It is probable that much of the snow at these great heights is evaporated rather than thawed.

the sky is generally clear, rain does not fall for the seven summer months, and Southern European fruits succeed admirably; and even the sugar-cane has been cultivated.* No doubt the plane of perpetual snow undergoes the above remarkable flexure of 9000 feet, unparalleled in other parts of the world, not far from the latitude of Concepcion, where the land ceases to be covered with foresttrees; for trees in South America indicate a rainy climate, and rain a clouded sky and little heat in

summer.

The descent of glaciers to the sea must, I conceive, mainly depend (subject, of course, to a proper supply of snow in the upper region) on the lowness of the line of perpetual snow on steep mountains near the coast. As the snow-line is so low in Tierra del Fuego, we might have expected that many of the glaciers would have reached the sea. Nevertheless, I was astonished when I first saw a range, only from 3000 to 4000 feet in height, in the latitude of Cumberland, with every valley filled with streams of ice descending to the seacoast. Almost every arm of the sea which penetrates to the interior higher chain, not only in Tierra del Fuego, but on the coast for 650 miles northwards, is terminated by "tremendous and astonishing glaciers," as described by one of the officers on the survey. Great masses of ice frequently fall from these icy cliffs, and the crash reverberates like the broadside of a man-of-war through the lonely channels. These falls, as noticed in the last chapter, produce great waves, which break on the adjoining coasts. It is known that earthquakes frequently cause masses of earth to fall from sea-cliffs: how

* Miers's Chile, vol. i., p. 415. It is said that the sugar-cane grew at Ingenio, lat. 320 to 330, but not in sufficient quantity to make the manufacture profitable. In the valley of Quillota, south of Ingenio, I saw some large date palm-trees.

FLOATING ICEBERGS.

317

furthest from the Pole, surveyed during the voyages of the Adventure and Beagle, is in lat. 46° 50', in the Gulf of Penas. It is 15 miles long, and in one part 7 broad, and descends to the seacoast. But even a few miles northward of this glacier, in the Laguna de San Rafael, some Spanish missionaries* encountered many icebergs, some great, some small, and others middle-sized," in a narrow arm of the sea, on the 22d of the month corresponding with our June, and in a latitude corresponding with that of the Lake of Geneva!

In Europe, the most southern glacier which comes down to the sea is met with, according to Von Buch, on the coast of Norway, in lat. 67°. Now this is more than 200 of latitude, or 1230 miles, nearer the pole than the Laguna de San Rafael. The position of the glaciers at this place and in the Gulf of Penas may be put even in a more striking point of view, for they descend to the seacoast within 70 of latitude, or 450 miles, of a harbour, where three species of Oliva, a Voluta, and a Terebra are the commonest shells, within less than 9° from where palms grow, within 440 of a region where the jaguar and puma range over the plains, less than 21from arborescent grasses, and (looking to the westward in the same hemisphere) less than 20 from orchideous parasites, and within a single degree of tree-ferns!

These facts are of high geological interest with respect to the climate of the northern hemisphere, at the period when boulders were transported. I will not here detail how simply the theory of icebergs being charged with fragments of rock explains the origin and position of the gigantic boulders of eastern Tierra del Fuego, on the high plain of Santa Cruz, and on the island of Chiloe. In * Agüeros, Desc. Hist, de Chiloe, p. 227.