The following pages present the results of a journey in Central Asia, among the mountains of Russian and Chinese Turkestan, during August and September, 1903, under the auspices of the Carnegie Institution of Washington. The purpose of the journey was specifically the determination of the later geological history of the region, and especially of the changes in the physical conditions of the country with respect to their influence on early human history. In the absence of any general knowledge of the physiography of the region it seemed advisable to undertake a reconnaissance in which the more obvious problems were examined, while those that required prolonged work in one place were deliberately set aside for future study. In pursuance of this plan, two months were spent in following the route shown on the accompanying sketch map (fig. 120), traveling slowly on horseback at the rate of scarcely 25 miles a day, and rarely staying in one locality over two nights. From the town of Przhevalsk, formerly known as Kara Kul, at the eastern end of Issik Kul or bake Issik, the road led (July 27) southwestward over the lofty Tian Shan plateau to Chadir Kul (August 6), thence southward, still among the mountains, to Shor Kul (August 15), and again southwestward across the border of the interior basin to Kashgar, the capital of Chinese Turkestan (August 21). The return journey led westward across the mountain spur between the Tian Shan and Alai ranges, via the Terek pass, 12,700 feet high, to Osh, in the Fergana basin of Russian Turkestan (September 5) ; then southwestward to Karategin in the Alai Mountains (September 18) ; and finally northward again, to Marghilan and the railroad (September 25). Although ten passes were crossed at a height of over 12,000 feet, the road on the whole was not one of great difficulty, and troublesome snow or ice was encountered in only three places. The district traversed measured about 350 miles from east to west, and 225 from north to south.