Page:Popular Science Monthly Volume 65.djvu/74

70 as also in a few islands of the Bay of Bengal and Arabia, and of western Asia. Numerous extinct volcanoes are found, not only in the same regions, but also in the Caucasus, on the plateau of Armenia, in east Tian-shan, in the northwestern border-ridges of the high Siberian plateau, and in the southwest of Aigun, in Manchuria (the Uyun Holdontsi region). An immense zone of land was covered with basaltic lavas during the early Tertiary period (or Cretaceous?) along the northwestern border of the high plateau of east Asia, and vents through which scoriæ were ejected, forming small cones of ejection, are still seen on the Mongolian and Vitim plateaus, as well as in the Sayans. Earthquakes are frequent, especially in Armenia, Turkestan and around Lake Baikal.

With the rich botanic materials which we are already in possession of, it would be extremely interesting to make a picture of the distribution of the different floras of Asia upon the surfaces of its high and lower plateaus, their border-ranges, the alpine zones, the high plains, and the lowlands. It would then appear how much these orographical divisions can help us to find out the true distribution of floras, which botanists have hitherto tried to bring into accordance with zones that were traced either along the degrees of latitude, or according to the basins of the different rivers, without taking into account the great orographical divisions and the differences of altitude, which mostly run in diagonal directions. Thus, to take only one example, the Great Khingan is the most important botanical boundary which is found all over Siberia and Manchuria. When one crosses this border-range and goes down its steep slope towards the east, one sees that in one hour, or maybe in half an hour, quite a new flora—Manchurian—takes the place of the Siberian flora; and one notices the appearance of trees, which strike even the most ignorant in botany, because these trees have not been seen before, while the traveler crossed Siberia over a distance of several thousand miles. One sees also how the Manchurian flora endeavors to spread westwards along the valleys of the Upper Amur and the Argun. Another important botanic boundary is the escarpment of the upper plateau, that is, the border-range of the Yablonovoi. This escarpment separates the Daurian flora from the Siberian, properly speaking, as sharply as the Great Khingan separates the Manchurian flora from the Daurian.

The Little Khingan will, I am inclined to think, also appear some day as another interesting botanic boundary between the Manchurian flora and the flora of the Pacific littoral. It is also quite certain that in central Asia, in the Gobi, in India and in western Asia, one could arrive at most interesting botanical generalizations by establishing the connection between the orographical and the botanical data; it is sufficient to mention here, as an instance, the delimitation of botanic