574 GEOLOGICAL REMARKS. 
and nature of the ranges, and the direction of the shores: the 
hills are irregularly heaped together ; the sounds are intricate and 
tortuous in their course, and the shores are formed by deep 
sinuosities and prominently projecting headlands: the channels, 
also, are studded with innumerable islands and rocks extremely 
dangerous for navigation. In this portion the rock is, for the 
most part, granite and greenstone. 
Near the centre of the Strait, the rock being clay-slate, the 
mountains are higher, and more precipitous and rugged in their 
outline ; and consequently not easily to be ascended. They are in 
general three thousand feet, but some are found to be four thou- 
sand feet, in height; and one, Mount Sarmiento, is upwards of 
six thousand feet high, and is covered throughout the year with 
snow. The line of perpetual snow in the Strait seems to be about 
three thousand five hundred feet above the sea: the mountains, 
whose height does not exceed three thousand, are, during the 
summer, frequently free from any, excepting in holes, where a 
large quantity is accumulated by drifting, and protected from the 
sun. The Strait here is quite free from islands, and it is a remark- 
able fact, that where the greenstone formation terminates, there 
the islands cease to appear. 
The slate formation continues as far as Freshwater Bay, where 
the stratified rocks leave the coast and extend in a north-west 
direction. The soil then becomes apparently a mixture of decom- 
posed slate and clay ; the slate gradually disappearing on approach- 
ing to Cape Negro, where the rock partakes of the character of 
the east coast. Here again we observe, along with the change of 
geological character, the re-appearance of islands, the soil of 
which is clayey, but with masses of granite, hornblende rock 
and clay slate protruding in many places through the superfi- 
cial soil, which, although it yields a poor grass, is entirely desti- 
tute of trees. 
In that portion of the Strait to the eastward of Cape Negro the 
hills are remarkable for the regularity and parallelism of their 
direction, and their general resemblance to each other. On the 
north shore, near Cape Gregory, a range of high land commences 
suddenly, with rather a precipitous ascent, and extends for forty 
miles to the north-east, where it terminates in detached rocky 
hills. The south-western end of the range is a ridge of flat-topped 
