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Updated: May 10, 2025
The great valley of the Mississippi and its tributaries forms the dividing territory between the volcanic and non-volcanic areas; so that on crossing the high ridges in which the western tributaries of America's greatest river have their sources, and to which the name of the "Rocky Mountains" more properly belongs, we find ourselves in a region which, throughout the later Tertiary times down almost to the present day, has been the scene of volcanic operations on the grandest scale; where lava-floods have been poured over the country through thousands of square miles, and where volcanic cones, vying in magnitude with those of Etna, Vesuvius, or Hecla, have established themselves.
Rivers shift their courses, coasts their outline, plains their level; volcanic peaks heighten or crumble; valleys are blocked by lava-floods or landslides; lakes appear and disappear.
Crossing to the east of the Grand Cañon, we find other lava-floods poured over the country at intervals, surmounted by San Francisco a volcanic mountain of the first magnitude which reaches an elevation, according to Wheeler, of 12,562 feet above the ocean. It has long been extinct, and its summit and flanks are covered with snow-fields and glaciers.
The old volcanoes glistened, for a wintry crust was widening over their long-dead ovens. Mount Saint Helens, as the far range which led up to the relic of the ancient lava-floods that is now known by that name was called by the settlers, was wonderfully beautiful in the twilights of the sun and moon.
The great outpourings of augitic lava of Tertiary and recent times which we have been considering appear to have been anticipated in several parts of the world, more especially in Peninsular India and in Africa, and it is desirable that we should devote a few pages to the description of these remarkable volcanic formations, as they resemble, both in their mode of occurrence and general structure, some of the great lava-floods of a more recent period we have been considering.
Of the districts to be described, the first which claims our notice is the Deccan. The vast area thus circumscribed is far from representing the original extent of the tract overspread by the lava-floods, as outlying fragments of these lavas are found as far east as long. 84° E. in one direction, and at Kattiwar and Cutch in another.
The floor upon which the lava-floods have been poured out generally consists of the "Cave Sandstone," the uppermost of a series of deposits which had previously been laid down over the bed of an extensive lake which occupied this part of Africa during the Mesozoic period.
Far back in the dim geologic ages, when the sediments of the old seas were being gathered and outspread in smooth sheets like leaves of a book, and when these sediments became dry land, and were baked and crumbled into the sky as mountain ranges; when the lava-floods of the Fire Period were being lavishly poured forth from innumerable rifts and craters; when the ice of the Glacial Period was laid like a mantle over every mountain and valley throughout all these immensely protracted periods, in the throng of these majestic operations, Nature kept her flower children in mind.
It is an isolated mountain, visible from afar, and reaches an elevation of 3110 feet, or nearly 800 feet above the surrounding plain. The above examples will probably suffice to afford the reader a general idea of the size and form of the volcanoes in this little known region. It has been stated above that the great lava-floods have probably been poured forth intermittently.
I would add another story to Mauna Loa's 16,000 feet if I could, and make it particularly bold and steep and craggy and forbidding and snowy; and I would make the volcano spout its lava-floods out of its summit instead of its sides; but aside from these non-essentials I have no corrections to suggest. I hope these will be attended to; I do not wish to have to speak of it again.
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