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Updated: May 29, 2025
Sir Archibald Geikie, F.R.S., in his elaborate monograph on the Tertiary Volcanic Rocks of the British Isles, has recorded his views regarding the origin and succession of the plateau basalts and associated rocks over the region extending from the north of Ireland to the Inner Hebrides; and in dealing with these districts in the following pages I have made extensive use of his observations and conclusions.
I even thought, with many other geologists, that obsidian, so far from being vitrified lava, belonged to rocks that were not volcanic; and that the fire, forcing its way through the basalts, the green-stone rocks, the phonolites, and the porphyries with bases of pitchstone and obsidian, the lavas and pumice-stone were no other than these same rocks altered by the action of the volcanoes.
In those days the rocks which are now the very bones and sinews of our mother earth her granites, her porphyries, her basalts, her syenites were melted into a liquid mass.
Unfortunately, strata of ferruginous earth conceal the soil from the researches of the geologist. It is only in some ravines, that we find columnar basalts, somewhat curved, and above them very recent breccia, resembling volcanic tufa. The breccia contain fragments of the same basalts which they cover; and it is asserted that marine petrifactions are observed in them.
Its length is 370 feet; and the height at the entrance of the cave is 117 feet. Thousands of majestic columns of basalts support a lofty roof, under which the sea rolls its waves, while the vastness of the entrance allows the light of day to penetrate the various recesses of the cave. The mind, says Mr.
These five rocks, dispersed over the whole globe, charged with oxidulated and titanious iron, are probably of similar origin. See MacCulloch in Edinburgh Journal of Science 1824 July pages 3 to 16. No volcanic rocks of a more recent period have hitherto been discovered in the island of Cuba; for instance, neither trachytes, dolerites, nor basalts.
From the inn-door we look abroad upon a mountain of basalts, covered on its summit by a forest of pines, and beautifully feathered along its face with birch-trees.
These basalts were covered with a mammiform substance, which I vainly sought on the Peak of Teneriffe, and which is known by the names of volcanic glass, glass of Muller, or hyalite: it is the transition from the opal to the chalcedony. We struck off with difficulty some fine specimens, leaving masses that were eight or ten inches square untouched.
The material is various boulders of granite and syenite; squares of trap and porphyry; the red sandstones of the Hisma; the basalts of the Harrah; and the rock found in situ, a brown and crumbling grit, modern, and still in process of agglutination.
He studied in the field, as well as by investigations in the laboratory, for fifteen years, with an intelligent and indefatigable perseverance, and, aided by the results of hundreds of analyses, eruptive masses of the most varied kind, the knowledge derived from which threw light upon the principles of science, from granites and syenites to melaphyres and basalts.
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