602 TIERRA DEL FUEGO. 
of expanding their stems and branches like the vegetation of warmer 
climates, they form a matted turf over a great part of the region. 
This turf is a foot thick, and is often dead below while green and 
flourishing above, resembling, in this respect, many mosses. It 
springs underfoot like the mossy surface of swampy grounds, and is 
actually soaked with water though appearing dry: a cane may almost 
anywhere be run down to a depth of three or four feet. Over much 
of the country there is a thick layer of imperfect peat below the vege- 
tation of the surface. Besides the smaller plants, a considerable part 
of the country is overgrown with stinted trees from six to twenty feet 
high. 
The moisture of the soil is derived mostly from the melting of 
snows, which cover the country the greater part of the year. ‘There 
are frequent pools of water standing in the valleys and on the elevated 
plains, and they are remarkable for having a rectangular or polygonal 
form as if works of art, and resembling the ponds often made in peat 
marshes. ‘The vertical sides of these ponds arise from the depth of 
the turf and peat below. ‘Their straight outline is explained with 
more difficulty. 
Rocks.—Along the coast from Orange Harbour to the head of Nas- 
sau Bay, there is a series of stratified deposits, which are here and 
there intersected by dikes of igneous rocks. ‘The latter generally 
form the summits of the hills. 
Sedimentary Rocks. 
The stratified rocks are parts of one formation, and consist of a fine- 
grained argillaceous shale, alternating with a sandstone more or less 
argillaceous and a coarse conglomerate. ‘The predominant colour of 
the shale is a dark bluish slate, which varies to a dull green. It 
cleaves readily into layers from a fourth of an inch to three or four 
inches thick, and is easily scratched with a knife. It passes insensi- 
bly into an argillaceous sandstone, having generally a dark dirt-brown 
colour, and consisting of layers seldom less than a foot in thickness. 
The conglomerates are composed of pebbles or boulders of soft 
argillaceous rocks, or of the igneous rocks of the region. In some in- 
stances these rocks have a calcareous cement; but in general, the 
pebbles are united by an argillaceous base. They have an earthy 
