Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.1): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

GEOLOGICAL REMARKS. 575 land covered with soil, but with here and there a protruding mass of primitive rock : one of these appeared to be of sienite or granite. The north-eastern end of this range is perhaps more bare of soil, and, therefore, exposes the rock, which shows itself in detached hills. Precisely similar in appearance and direction is a range on the south shore, about fifty miles in length, commencing at Cape Monmouth and terminating in detached hills in the vicinity of the south side of the First Narrow. The courses, also, of both the First and Second Narrow, which are just within the eastern entrance of the Strait, are nearly parallel with these hills ; and the smaller ranges of eminences, Elizabeth Island and the cliffy land of Cape Negro, where the clay formation commences, all trend to the N.N.E., preserving a general resemblance of form and character to the two ranges above mentioned. The irregularity of the topographic features of the western por- tion of the Strait, combined with its confused assemblage and im- mense number of islands and rocks ; — the regularity of the strata — the coinciding parallelism of all the bays, channels, and sounds, — and the total absence of islands in the central portion or slate formation ; — together with the remarkable similarity of the direc- tion of the hills and coast line, and the stratification of the north- eastern tract, which is very different from that of the centre ; are very striking facts, and, geologically considered, are of great interest. No less remarkable, however, and equally interesting, is the character of the vegetation ; not so much in the variety of plants, as in their stunted growth to the westward, their luxuriance in the centre, and the total absence of trees to the eastward. For this mo- dification the following reasons seem to me to account sufficiently. To the westward the decomposition of granite, and the other pri- mitive rocks which are found there, forms but a poor, unproductive soil ; so that, although the land is thickly covered with shrubs, they are all small and stunted: the torrents of water also that pour down the steep sides of the hills, wash away the partial accumula- tions of soil that are occasionally deposited ; consequently, few trees are to be found, excepting in clefts and recesses of the rock, where decomposed vegetable matter collects and nourishes their growth ; but even there they are low and stunted, for the most luxuriant seldom attain a larger diameter than nine or ten inches. 2 p2