Page:Transactions NZ Institute Volume 10.djvu/34

19 alternately to or from the north, introducing antarctic fauna into the northern hemisphere during one cycle, and arctic at another into the southern temperate zone. Their respective remains, intermingled at first in the upper strata with those of tropical and sub-tropical forms, are now being deposited layer upon layer over the beds which contain such different ones below, and which will again in many places come to entomb the shells and the bones of races similar in type to those which previously there found a grave, when such a change in temperature as has occurred in most regions over and over again takes place.

The most enthusiastic glacialist could ask for no mightier engine than the great antarctic stream bearing its vast islands of ice sixty miles and more in length far towards the tropics in certain meridians.

What local influences are doing now in northern regions, students have more ample opportunity of observing. Notably the condition of great part of Greenland, where, in latitude 70°, ice islands of enormous dimensions float off from a sea-cliff of solid glacier ice 3,000 feet in height. The state of things obtaining in that great land may be contrasted with that in the equally misnamed country, Iceland, even that of its lower portions in 65° N. with that of Lapland in 72°. The climate of the Crimea affords a useful example when compared with that of Venice or Bordeaux. In consequence of the radiation from the Thibetan steppes, we find cereals ripening on the Siberian side of the Himalaya at a height above the sea equal to that of the summit of Mont Blanc, whilst several thousand feet lower down arctic cold prevails, and mighty glaciers do their work above the burning plains of Hindostan, growing under the soft breath of the rain-bearing southerly winds.

Again intense cold prevails over countries on the shores of that great inlet of the North Pacific which, in not very remote times, teemed with animal life of southern types.

In that region where the Amoor river after flowing amidst umbrageous groves and vine-clad hills turns north and enters a frozen sea, a local glacial period has possibly commenced, advancing with slow but unwavering steps, which might easily be accelerated by the subsidence of the shallow sea-bottom which interrupts the flow of polar waters; whilst in other places owing to a deviation in the direction of local currents of warm and chilled waters in seas of no great depth, sub-tropical forms are again multiplying where but recently arctic ones usurped possession.

The iron grasp of frost has loosened its hold over great part of Western America, and a temperate climate for ages has been gaining sway over the arid regions where rivers flow in deep chasms or canons worn by them through the plains under the Rocky Mountains.