Geology. 249 



to support the supposition that in early Pleistocene time the Alai 

 mountains wasted down until a detritus-covered piedmont plain 

 formed on the north of the range, whereupon a dislocation seems 

 to have occurred nearly parallel to the range and north of it with 

 sinking of the plains still farther north or with uplift of the 

 range. The relations of the river work to this change of altitude 

 are briefly explained. 



In his article on central Turkestan Mr. Huntington gives a 

 summary of the geology and topographic development. Of the 

 Paleozoic series he states: "In Central Turkestan a single suc- 

 cession of strata is repeated again and again, with only slight 

 local modifications. The oldest observed formation is an ancient 

 white marble, shot through and through with intrusions of gran- 

 ite. It was noticed only in the Alai Mountains in the neighbor- 

 hood of Kok Su and Karategin. Its junction with the overlying 

 formation was not seen, but the contact presumably shows an 

 unconformity, as a conglomerate near the base of the covering 

 strata contains pebbles of the marble. The granite which is 

 intruded into the marble is of much later date, for it occurs 

 abundantly in the Paleozoic series in the ridges of the Tian Shan 

 plateau and along the north side of the Alai range. The main 

 body of the Paleozoic series is a great thickness of limestones, 

 many of them slaty, which are stated by Tchernachef to be of 

 Devonian and Carboniferous age. They are greatly folded and 

 have been penetrated not only by granite intrusions, but also by 

 some basaltic lavas, as may be seen, for instance, in the Sugun 

 Valley west of Shor Kul. The folding of the Paleozoic strata 

 is of the sort which is associated with mountain building, hence 

 at the end of tl?e Paleozoic era or in the early part of the Meso- 

 zoic this part of Central Asia must have been highly mountain- 

 ous. In evidence of this it may be pointed out that the succeed- 

 ing unconformable conglomerates are so coarse that they could 

 only have been formed subaerially in a region of considerable 

 relief, and yet at the time of their deposition the old folds of 

 limestone and slate had already suffered great denudation. As a 

 rule, the hard Paleozoic strata are found in the highlands, while 

 the softer Mesozoic and Tertiary strata occur in basins among 

 the highlands and mountains ; but this seems due less to the 

 superior resistance of the older rocks than to the fact that they 

 were bent down where they are covered, and that the younger 

 strata were largely formed in the very basins which they now 

 occupy." 



" The conditions under which the Mesozoic-Tertiary series were 

 deposited seem to have been largely subaerial, or at least non- 

 marine. The coarse conglomerates at the base probably indicate 

 arid or semi-arid conditions in a region of considerable relief. 

 As relief grew less, or as the climate grew moister, the gravel of 

 the conglomerate gave place to sand, and that in turn to shale ; 

 in the latter are four or five coal seams. The next period, that 

 of the vermilion beds, seems to have opened at a time of sub- 



Am. Jour. Sci. — Fourth Series, Yol. XX, No. \Y\. — September, 1905. 



