The heart of the great Asiatic continent is cut off by great mountain ranges from the rainy monsoons of the Indian and China seas, while the mountains and plateaux of Europe deplete the lighter store of moisture in the westerly winds from the Atlantic and Mediterranean. So it is that despite the enormous neight of its fnountain chains and the great elevation of the plateaux there is a vast track of country from the Volga river to the Hwang Ho and the Great Wall of China in which forests are found only as narrow girdles on the slopes of the higher ranges and rivers dwindle yearly after the melting of mountain snows.