Page:Popular Science Monthly Volume 43.djvu/270

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which, suggested Murchison's view. The displacements were accompanied by modifications of the rocks, of which Geikie wrote that "in exchange for this (Murchison's) abandoned belief we are presented with startling new evidence of original metamorphism on a colossal scale, and are admitted some way into the secret of the processes whereby it has been produced."

Sir Archibald Geikie's chief geological work, according to the estimate of Nature, seems to be his exhaustive review of the volcanic history of the British Isles. The northwestern part of Great Britain is marked, like the Snake River region in our own country, by the evidences of the outpouring over the land of immense sheets of lava, which in the present instance took place in Tertiary times. Sir Archibald made it his task in the investigation of this phenomenon "to discern the site of the centers of eruption, and determine the old chimneys, the remnants of which give a glimpse into the lowest parts of ascending lavas; to discriminate the volcanic necks, the intrusive sheets and dikes, the bedded lavas and the tuffs." Evidences of still earlier volcanic activity were also found in the Old Red Sandstone of Scotland, and in the oldest formations of England and Wales. In order to prepare himself more thoroughly for the investigation of this phenomenon, Mr. Geikie traveled over much of Europe, from northern Norway to the Lipari Islands; then came over to Canada and the United States, and followed the course of our geological surveys, particularly in the Western States and Territories and the lava-covered regions. In another department of the same investigation he gave more attention to petrological studies than any Englishman had done before him. Besides giving rise to many valuable memoirs relating directly to what he had seen and observed, these studies contributed greatly to the enlargement of Prof. Geikie's views and to the increase of the breadth of his work; and some of their results may be seen in the greater richness of illustration apparent in his subsequent writings. Their mature fruit is presented as a whole in his presidential addresses of 1891 and 1892. He was especially interested, they being exactly in the line of his principal study, in the lava beds of Snake River; and in his essay on the Lava Fields of Northwestern Europe refers to them as the site which first enabled him to realize the conditions of volcanic action described by Richtofen—the emission of vast floods of lava without formation of cones and craters—and, without acquiescing in all that author's theoretical conclusions, to judge of the reality of the distinction "which he rightly drew" between massive eruptions and ordinary volcanoes with cones and craters.

We have referred to Prof. Geikie's work in tracing the origin of the present shaping of land surfaces and of natural scenery to its geological factors as constituting one of his special titles to