Page:Popular Science Monthly Volume 42.djvu/296

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THE POPULAR SCIENCE MONTHLY.

ultimately become known. The island has furnished such an abundance of important and prominent new types, that, as respects plant life, it may be regarded as one of the most interesting and beautiful parts of the earth. The close relationship often supposed to exist between the north Australian flora and that of New Guinea has not been confirmed. It is true that the savannas of the Fly River, covered with eucalyptuses, myrtaceæ, and proteaceæ, correspond not only in their outward habitus, but also in composition, with the formation of York Peninsula; but the typical Australian flora is quite foreign to New Guinea, and there is no ground for the supposition that the island was at one time inhabited by Australian species. The palm flora of the island is one of the richest in the world; almost every district is distinguished by endemic species. The age of the island must be very great; the large number of indigenous genera and species testify to this; of the former, at least fifty are already known.

 

Geographical Development of Coast-lines.—Summing up the points of his paper in the British Association on the Geographical Development of Coast-lines, Prof. James Geikie arrives at the general conclusion that the coast-lines of the globe are of very unequal age. Those of the Atlantic were determined as far back as Palæozoic times by great mountain uplifts along the margin of the continental plateau. Since the close of that period many crustal oscillations have taken place, but no grand mountain ranges have again been ridged up on the Atlantic seaboard. Meanwhile the Palæozoic mountain-chains, as was shown, have suffered extensive denudation, have been planed down to the sea-level, and even submerged. Subsequently converted into land, wholly or partially as the case may have been, they now present the appearance of plains and plateaus of erosion, often deeply indented by the sea. No true mountains of elevation are met with anywhere in the coast-lands of the Atlantic, while volcanic action has well-nigh ceased. In short, the Atlantic margins have reached a stage of comparative stability. The trough itself, however, is traversed by at least two well-marked banks of upheaval—the great meridional Dolphin Ridge, and the approximately transmeridional Faröe-Icelandic belt—both of them bearing volcanic islands. But while the coast-lands of the Atlantic proper attained relative stability at an early period, those of the Mediterranean and Caribbean depressions have up to recent times been the scenes of great crustal disturbance. Gigantic mountain-chains were uplifted along their margins at so late a period as the Tertiary, and their shores still witness volcanic activity. It is upon the margins and within the troughs of the Pacific Ocean, however, that subterranean action is now most remarkably developed. The coast-lines of that great basin are everywhere formed of grand uplifts and volcanic ranges, which, broadly speaking, are comparable in age to those of the Mediterranean and Caribbean depressions. Along the northeast margin of the Indian Ocean the coast-lines resemble those of the Pacific, being of like recent age, and similarly marked by the presence of numerous volcanoes. The northern and western shores, however (as in Hindostan, Arabia, and East Africa), have been determined rather by regional elevation or by subsidence of the ocean floor than by axial uplifts—the chief crustal disturbances dating back to an earlier period than those of the East Indian Archipelago. It is in keeping with this greater age of the western and northern coast-lands of the Indian Ocean that volcanic action is now less strongly manifested in their vicinity.

 

The Story which Scenery tells.—"The law of evolution," said Prof. Archibald Geikie at the British Association, "is written as legibly on the landscapes of the earth as on any other page of the book of Nature. Not only do we recognize that the existing topography of the continents, instead of being primeval in origin, has gradually been developed after many precedent mutations, but we are enabled to trace these earlier revolutions in the structure of every hill and glen. Each mountain-chain is thus found to be a memorial of many successive stages in geographical evolution. Within certain limits, land and sea have changed places again and again. Volcanoes have broken out and have become extinct in many countries long before the advent of man. Whole tribes of plants and animals have meanwhile come and gone, and in leaving their remains behind them as