This region, which slopes westwards and northwards to the Caspian, Aral, and Balkhash, is about equally divided into a lowland and highland district. Climate, flora, and fauna vary as much as the geological formations in a land rising in some places to elevations of 20,000 and 22,000 feet in others, as along the Caspian shores, sinking below sea-level. Nevertheless a certain analogy is maintained between the eastern highlands and the western lowlands. In both cases the annual variation of temperature is greater than in Europe or in any other sea-girt land. In autumn and winter the north-east polar blasts prevail on the plains and uplands, giving place in spring and summer to the hot equatorial winds from the south-west. Thus the normal climate of each season becomes intensified here as elsewhere in the interior of the continent, so that in July this region is included in the isothermals of 20° to 25° Centigrade, a temperature answering to that of the Cape Verd Islands, 1,650 miles nearer to the equator, while in January the isothermals are those of Canada, South Greenland, and Spitzbergen, some 1,800 miles nearer to the North Pole. But the variation between the hottest and coldest days is even still greater, averaging no less than 130°, or from about 111° to −12° and even −20° Fahr. On the plains the dryness of the atmosphere and absence of dew add to the rigours of the climate. Whole years have passed without any rainfall, and in 1858 the rains lasted only four hours altogether in the Kara-kum Desert. The moisture borne by the south-west breezes is precipitated on the slopes of the Pamir and in the Tian-shan valleys; but even here the discharge is relatively far less than on the European and Indian highlands.
Another characteristic of Russian Turkestan is the continuous drying up of the soil going on throughout the whole of the present geological epoch. The twin rivers, Oxus and Sir-daria, flowing from the Pamir and Tian-shan nearly parallel to each other, at present discharge their waters into the Aral Sea; but these formerly far more copious streams united in a common channel, disemboguing in the Caspian. Though still ranking in length amongst the great Asiatic rivers—over 1,200 miles each—they are far inferior in volume to the Siberian, Chinese, and Indian streams flowing seawards. Their basins show evident signs of gradual absorption—old channels now partially filled up, numerous rivers formerly reaching the main streams, but now lost in the sands, or expanding into brackish morasses, thousands of lakelets now indicated only by saline incrustations. Even the large inland seas, such as Aral and Balkhash, have diminished in size, while others have been replaced by the Kulja and Ferghana plains. Owing to this continually increasing dryness a large portion of the country has been transformed to steppe lands even on the higher grounds, as on the Pamir, Tian-shan, and Tarbagatai, where the growth of vegetation is limited to three months, partly by the winter snows, partly by the summer droughts.
