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In a W. by S. direction from these, and distant four or five miles, is another peak, to which I gave the name of "Macarthur's Peak," after Mr. William Macarthur, of Cambden. All these peaks are composed of Domite; and Roper's and Scott's Peaks are surrounded by a sandstone formation, covered with a dense low scrub.
I did not ascend Mount McConnel, but it seemed to be composed of a species of domite. On the subordinate hills I observed sienite. The bed of the river furnished quite a collection of primitive rocks: there were pebbles of quartz, white, red, and grey; of granite; of sienite; of felspathic porphyry, hornblende, and quartz-porphyry; and of slate-rock. The morning was cloudless.
This division corresponds with that proposed by Bunsen and Durocher for volcanic rocks, upon the results of analyses of a large number of specimens from various districts. Examples: Basalt, Dolerite, Hornblende rock, Diorite, Diabase, Gabbro, Melaphyre, and Leucite lava. Examples: Trachyte, Rhyolite, Obsidian, Domite, Felsite, Quartz-porphyry, Granite.
That is to say, the surfaces of the lava-streams are not at all, or only slightly, decomposed into soil suitable for the growth of plants, except in rare instances. E. G. Hull, "On the Domite Mountains of Central France," Scien. Proc. Roy. Dublin Society, July 1881, p. 145. Dr. Hull determined the density of the domite of the Puy de Dôme to be 2.5, while that of lava is about 3.0.
The dome-shaped volcanoes are generally composed of felsitic matter, whether domite, trachyte, or andesite, which has been extruded in a molten or viscous condition from some orifice or fissure in the earth's crust, and being piled up and spreading outwards, necessarily assumes such a form as that of a dome, as has been shown by experiment on a small scale by Dr. E. Reyer, of Grätz.
In the case of the Puy de Dôme there is some evidence that the domite matter rests on a basis of ashes and scoriæ, which may be seen in a few places around the base of the cone. It is difficult without some such theory as this to explain how a viscous mass was able to raise mountains some 2000 or 3000 feet above the surrounding plain.
Although we passed many localities where water might have been expected, and travelled where three different rocks, domite, sandstone, and basalt, came in contact, and where springs are so frequently found, yet not a drop of water could we find.
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