Page:Popular Science Monthly Volume 39.djvu/683

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HE sea, in its vastness, reaching far beyond the encircling flat horizon, is a better symbol of infinitude and of eternity than is the most majestic mountain range, lifting its serrated forehead miles above the ocean-level and seeming almost to pierce the sky. The sea itself, but no part of the land forming its shores, has continued unchanged through the series of geologic eras.

 "Time writes no wrinkle on thine azure brow— Such as creation's dawn beheld, thou rollest now."

But on the land, no sooner have the subterranean forces upheaved a mountain, a plateau, a continent, or an island, than the processes of subaërial erosion begin to contend against it. Rains, frost and heat, chemical change, subdue the most enduring and solid rock formations, dividing them with fractures, and pulverizing their masses and fragments to sand and clay, which gravitation by the vehicle of running water carries down and away to the sea, there to find rest until another uplift shall renew the cycle of changes. "The mountain falling cometh to naught, and the rock is removed out of his place."

The form of mountains and of their ranges and systems is due to the combination, in varying ratios, of constructive and destructive agencies. The first only seem necessary; but the second have generally been far more efficient to give the shape and outlines of all our mountains, excepting volcanoes. Constructive forces have done work that may be compared to the quarrying of the block of marble and bringing it to the artist's studio; destructive forces, producing the present mountain forms, as they stand before our vision, have done work like chipping away the greater part of the marble block and chiseling it to the finished statue. It will be convenient to speak of the constructive processes as mountain-building, and of the destructive as mountain-sculpture.

It is from observation and study of the geologic structure of mountain ranges, the diverse rock formations of which they are composed, and their attitude and relationship to each other, that we discover and understand their origin; how, by what agencies, the mountains have been built and sculptured. Structure and origin are thus very intimately connected and demand the same division under classes and types. In this classification, when citing examples of each type, we can commonly note also their