CONCLUSION. I 17
Many problems that are touched upon in this and the following reports deserve much more study than we have been able to give them thus far. Some of them bear directly upon the objects of our expedition ; some are of general interest. Of the first class, the oscillations of the Caspian stand preeminent, and the desert depression, known as the Ungus, seems to be the most important district for next examination in this connection. In view of what is known of climatic variations during Quaternary time in other parts of the world, it is hardly possible that the Aralo-Caspian history is of only one expansion; and whatever complications it experienced would probably have left their record on the bluffs and slopes that border this desert depression. At the saine time, the confirmation of our conclusions regarding the complexity of the Glacial period by further study of moraines and terraces, especially in the Alai ranges and the Pamir, is much to be desired. Then would come the connection of these two classes of unlike records—lacustrine and glacial—by any means that can be devised, along the mountains on the south or across the desert plains, thus gaining a correlation of the events of Quaternary time in the three physiographic provinces of the western Asiatic region and bringing the archeological remains of the plains into their place on the geological time-scale. Of subordinate value, but by no means unimportant, are the problems connected with the deposits of loess. Those south of Jizak deserve first attention.
Issik Kul is a problem by itself. Geology, physiography, and archeology are there combined in the most inviting manner. A long season in that field alone would be highly productive.
An outstanding problem of importance in its bearing on theoretical geology is found in the structure of the Tian Shan ranges. For this purpose the region, could . be entered to advantage from the north, and a deliberate study made of the pene-plains and fault-block mountain ranges over which our party had to pass so rapidly. Few finer fields are open to the investigator.