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These rocks approach towards true granites in one direction, and through quartz-porphyry and felsite to rhyolite in another probably depending upon the conditions of cooling and consolidation. In their mode of weathering and general appearance on a large scale, they present a marked contrast to the basic lavas with which they are in contact from the coast of L. na Keal to that of L. Buy.
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.
Similar masses occur in North Mayo, south of Belderg Harbour. Cambrian Period. In the Pass of Llanberis, along the banks of Llyn Padarn, masses of quartz-porphyry, felsite and agglomerate, or breccia, indicate volcanic action during this stage. These rocks underlie beds of conglomerate, slate and grit of the Lower Cambrian epoch, and, as Mr.
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