Part 19

See The Abundance of Life.

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when it is done with vitality, for that preparation for momentous organic events which is in progress throughout the entire course of development; and to the economy involved in the welding of physiological processes for the phenomenon of physiological memory, wherein we see reflected, as it were, in the development of the organism, the association of inorganic restraints occurring in nature which at some previous period impressed itself upon the plastic organism. We may picture the seedling at Upsala, swayed by organic memory and the inherited tendency to an economical preparation for future events, gradually developing towards the aesthetic climax of its career. In some such manner only does it appear possible to account for the prophetic development of organisms, not alone to be observed in the alpine flowers, but throughout nature.

And thus, finally, to the effects of natural selection and to actions defined by general principles involved in biology, I would refer for explanation of the manner in which flowers on the Alps develop their peculiar beauty.

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MOUNTAIN GENESIS

OUR ancestors regarded mountainous regions with feelings of horror, mingled with commiseration for those whom an unkindly destiny had condemned to dwell therein. We, on the other hand, find in the contemplation of the great alps of the Earth such peaceful and elevated thoughts, and such rest to our souls, that it is to those very solitudes we turn to heal the wounds of ife. It is difficult to explain the cause of this very different point of view. It is probably, in part, to be referred to that cloud of superstitious horror which, throughout the Middle Ages, peopled the solitudes with unknown terrors; and, in part, to the asceticism which led the pious to regard the beauty and joy of life as snares to the soul's well-being. In those eternal solitudes where the overwhelming forces of Nature are most in evidence, an evil principle must dwell or a dragon's dreadful brood must find a home.

But while in our time the aesthetic aspect of the hills appeals to all, there remains in the physical history of the mountains much that is lost to those who have not shared in the scientific studies of alpine structure and genesis. They lose a past history which for interest com-

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petes with anything science has to tell of the changes of the Earth.

Great as are the physical features of the mountains compared with the works of Man, and great as are the forces involved compared with those we can originate or control, the loftiest ranges are small contrasted with the dimensions of the Earth. It is well to bear this in mind. I give here (Pl. XV.) a measured drawing showing a sector cut from a sphere of 50 cms. radius; so much of it as to exhibit the convergence of its radial boundaries which if prolonged will meet at the centre. On the same scale as the radius the diagram shows the highest mountains and the deepest ocean. The average height of the land and the average depth of the ocean are also exhibited. We see how small a movement of the crust the loftiest elevation of the Himalaya represents and what a little depression holds the ocean.

Nevertheless, it is not by any means easy to explain the genesis of those small elevations and depressions. It would lead us far from our immediate subject to discuss the various theoretical views which have been advanced to account for the facts. The idea that mountain folds, and the lesser rugosities of the Earth's surface, arose in a wrinkling of the crust under the influence of cooling and skrinkage of the subcrustal materials, is held by many eminent geologists, but not without dissent from others.

The most striking observational fact connected with mountain structure is that, without exception, the ranges

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of the Earth are built essentially of sedimentary rocks: that is of rocks which have been accumulated at some remote past time beneath the surface of the ocean. A volcanic core there may sometimes be--probably an attendant or consequence of the uplifting--or a core of plutonic igneous rocks which has arisen under the same compressive forces which have bowed and arched the strata from their original horizontal position. It is not uncommon to meet among unobservant people those who regard all mountain ranges as volcanic in origin. Volcanoes, however, do not build mountain ranges. They break out as more or less isolated cones or hills. Compare the map of the Auvergne with that of Switzerland; the volcanoes of South Italy with the Apennines. Such great ranges as those which border with triple walls the west coast of North America are in no sense volcanic: nor are the Pyrenees, the Caucasus, or the Himalaya. Volcanic materials are poured out from the summits of the Andes, but the range itself is built up of folded sediments on the same architecture as the other great ranges of the Earth.

Before attempting an explanation of the origin of the mountains we must first become more closely acquainted with the phenomena attending mountain elevation.

At the present day great accumulations of sediment are taking place along the margins of the continents where the rivers reach the ocean. Thus, the Gulf of Mexico receiving the sediment of the Mississippi and Rio Grande;

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the northeast coast of South America receiving the sediments of the Amazons; the east coast of Asia receiving the detritus of the Chinese rivers; are instances of such areas of deposition. Year by year, century by century, the accumulation progresses, and as it grows the floor of the sea sinks under the load. Of the yielding of the crust under the burthen of the sediments we are assured; for otherwise the many miles of vertically piled strata which are uplifted to our view in the mountains, never could have been deposited in the coastal seas of the past. The flexure and sinking of the crust are undeniable realities.

Such vast subsiding areas are known as geosynclines. From the accumulated sediments of the geosynclines the mountain ranges of the past have in every case originated; and the mountains of the future will assuredly arise and lofty ranges will stand where now the ocean waters close over the collecting sediments. Every mountain range upon the Earth enforces the certainty of this prediction.

The mountain-forming movement takes place after a certain great depth of sediment is collected. It is most intense where the thickness of deposit is greatest. We see this when we examine the structure of our existing mountain ranges. At either side where the sediments thin out, the disturbance dies away, till we find the comparatively shallow and undisturbed level sediments which clothe the continental surface.

Whatever be the connection between the deposition and

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the subsequent upheaval, the element of great depth of accumulation seems a necessary condition and must evidently enter as a factor into the Physical Processes involved. The mountain range can only arise where the geosyncline is deeply filled by long ages of sedimentation.

Dana's description of the events attending mountain building is impressive:

"A mountain range of the common type, like that to which the Appalachians belong, is made out of the sedimentary formations of a long preceding era; beds that were laid down conformably, and in succession, until they had reached the needed thickness; beds spreading over a region tens of thousands of square miles in area. The region over which sedimentary formations were in progress in order to make, finally, the Appalachian range, reached from New York to Alabama, and had a breadth of 100 to 200 miles, and the pile of horizontal beds along the middle was 40,000 feet in depth. The pile for the Wahsatch Mountains was 60,000 feet thick, according to King. The beds for the Appalachians were not laid down in a deep ocean, but in shallow waters, where a gradual subsidence was in progress; and they at last, when ready for the genesis, lay in a trough 40,000 feet deep, filling the trough to the brim. It thus appears that epochs of mountain-making have occurred only after long intervals of quiet in the history of a continent."

Dana, Manual of Geology, third edition, p. 794

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