more highly warped and the red deposits were also uplifted along the borders of the basin and were exposed to erosion. Meanwhile the superficial deposits which now cover the plains were laid down and the country assumed its present form. It is not to be supposed that every basin has gone through exactly the same process, or that a single process has everywhere taken place at the same time. Accidents have intervened. At Zorabad the damming of the Heri Rud formed a lake and greatly altered the course of events. At Sistan, and probably elsewhere, a series of lakes appears to have occupied the basin during the glacial period. Nevertheless the general course of events was a gradual progress from larger basins to smaller basins, and from subaqueous to subaerial deposition."
Von dem Oberflächenmaterial meldet der Verfasser : „Proceeding from the coarser to the finer deposits, we find that the center of each basin usually holds a salt lake or playa, bordered by an area of fine silt." — Groberer Sand kommt jedoch als Beimengung bei den feinsten Ablagerungen vor.
Schließlich stellt der Verfasser über die Verhältnisse in Seistan eine Theorie auf, die er „Fluvial or Lacustral Theory" nennt: „The theory which explairls the phenomena of Sistan by a succession of fluvial and interfluvial epochs is an expansion of the principles which have become so well established in the study of the glacial phenomena of Europe and North America. During fluvial or lacustral epochs the increased rainfall or decreased evaporation would cause a large lake on the basin of Sistan ; the streams from the surrounding mountains would become fuller or more perennial, vegetation would become more abundant, and the mountain slopes would tend to become graded. As a result of all this load of the stream would be fine in texture and would be carried quickly to the lake, where it would be deposited without having an opportunity to become highly weathered. The lake bottom would be covered with unoxidized clays of fine texture and light colour. On the advent of an interfluvial epoch, the lake would decrease in size, and marshes would encroach upon its edges; the rivers would dwindle and become intermittent, and at the same time would become subject to fiercer floods; vegetation would everywhere decrease; and the slopes would become ungraded. These changes would allow coarser materials, such as sand and even gravel, to be washed in over the exposed portions of the old lake bed. The total amount of material might be greater than during the moister period, for the flood torrents would be loaded to the utmost ; but the journey of a given particle would be much slower, for the laden floods would quickly spread into a sheet and deposit their loads, and many short journeys separated by long periods of exposure would be required to bring the waste of the mountains to its final resting place. During this protracted journey the redness which characterizes the fluviatile strata would be acquired through oxidization. A succession of ten fluvial and inter-fluvial epochs would account for all the observed facts of the clays of Sistan. There
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