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0288 Explorations in Turkestan 1903 : vol.1
Explorations in Turkestan 1903 : vol.1 / Page 288 (Color Image)

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doi: 10.20676/00000177
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better, gravel, forming an unconsolidated sheet some 4o or 5o feet thick, which lies unconformably on the beveled edges of the other strata and shows almost no sign of warping. It seems probable, however, that the gravel sheet has been uplifted and tilted somewhat, and that it represents the old piedmont deposit of a time previous to the faulting and uplift of the Anau and Suru-Muzdar blocks. On the east this conglomerate or, better, gravel, forms a smooth though sloping plain, in whic?i are incised young valleys ; on the west it has been dissected into low, rolling hills.

Thus far there can be but little question as to the true nature and origin of the phenomena of the gorge ; it is when we come to the terraces that the difficulty begins. In its more open portions to the north of the hard limestone the sides of the gorge are marked by well-defined gravel terraces to the number of five, which gradually converge downstream until they, as well as the upper grade plain, merge into the general slope of the present piedmont plain in the vicinity of Anau, where the stream comes to an end. The heights of the terraces above the stream, as measured at a point well within the gorge a little below the so-called Old Mills," are approximately as follows :


First terrace, narrow and insignificant    3

Second terrace, rather 'broad and strong ..   6
Third terrace, broad plain of main valley floor 20

Fourth terrace, narrow, often missing    5o
Fifth terrace, broad and flat ioo

Grade plain, uplifted piedmont deposit    300

The whole number of terraces is not always present, sometimes one and sometimes another being undercut ; nor does it appear as though they all merged into the plain at the same point.

If all the terraces were cut in the solid rock, and came to an end in the Anau fault block, it would be easy to explain them as the product of the saine faulting

which produced the block and which uplifted the old piedmont plain. As a matter

of fact, however, the lower terraces at least, so far as their structure could be made out, seem to be composed entirely of stream-laid gravel. In other words, the gorge

was cut to nearly its present form and then was subjected to a series of changes by which it was first filled with gravel and then cut out again. Moreover, although the terraces disappear in the narrowest portion of the gorge, three of them reappear in the more open portion of the valley farther upstream—another evidence that the younger ones are of later date than the gorge. The importance of the relative ages of the gorge and the terraces lies in the fact that the fault which caused the cutting of the gorge represents the last movement of uplift of which we have any unmistakable record. It is not impossible that the terraces are due to earth movements of a kind which first caused deposition and then erosion, this alternation being repeated as many times as there are separate gravel deposits, an unknown quantity which may number from one to five. The Anau terraces, like those described by Professor Davis, are unsatisfactory, because, so far as can be seen, they may be either tectonic or climatic in origin.

At Anau, and elsewhere along the base of the mountains as far as Dushak, where the railroad turns to the northeast, the hasty view of the country obtained