The apparently artificial formation of this channel is very striking. It seems to have been formerly a valley between two ridges of the range, in the direction of the strata (of which there are frequent instances, such as the valley in the Lomas Range, opposite Cape San Isidro, the valley of Valdez Bay, and one immediately to the north of the channel itself, besides many others), and that at some remote period the sea had forced its way through, effecting a communication between the Strait and the waters behind Dawson Island: as if one of those great 'northern waves,' of which we once heard so much, had rolled down the wide reach of the Strait (the parallelism of whose shores is also remarkable) from the north-west, towards Cape Froward; and finding itself opposed by the Lomas Range, had forced a passage through the valley until stopped by the mountains at Fitton Bay. Having imagined such a wave in motion, the reader may fancy it uniting with another northern roller from Cape San Valentyn, attacking the hills and carrying all before it, until Mount Hope, at the bottom of Admiralty Sound, arrested its course. I have already noticed the remarkably straight direction in which this curious channel trends. At both extremities the width may be from two to three miles; but the shores gradually approach each other midway, and the coast on each side rises abruptly to the height of fifteen hundred feet. The south shore, sheltered from the prevailing and strongest winds, is thickly covered with trees and luxuriant underwood, which, being chiefly evergreen, improve {50} the scenery greatly, particularly in the winter season: the north shore is also well wooded for about two-thirds up; but the summit is barren and the outline very much serrated, as is usual in slate formations. On the north shore we noticed some extraordinary effects of the whirlwinds which so frequently occur in Tierra del Fuego. The crews of sealing vessels call them 'williwaws,' or 'hurricane-squalls,' and they are most violent. The south-west gales, which blow upon the coast with extreme fury, are pent up and impeded in passing over the high lands; when, increasing in power, they rush violently over the edges of precipices, expand, as it were, and descending perpendicularly, destroy every thing moveable. The surface of the water, when struck by these gusts, is so agitated, as to be covered with foam, which is taken up by them, and flies before their fury until dispersed in vapour. Ships at anchor under high land are sometimes suddenly thrown over on their beam-ends, and the next moment recover their equilibrium, as if nothing had occurred. Again a squall strikes them, perhaps on the other side, and over they heel before its rage: the cable becomes strained, and checks the ship with a jerk, that causes her to start a-head through the water, until again stopped by the cable, or driven astern by another gust of wind.