OASES. 329 
Irrigation sediments are of course far more widespread than culture, while 
between them there is a gradation which may be termed garden culture—sedi- 
ments arising from the concentrated irrigation of gardens in and near a city and 
thus more rapid in growth than those of ordinary fields and containing many 
artefacts. These are all well exposed in gullies near the citadel of Anau. Irriga- 
tion stuff proper is at first hard to distinguish from natural alluvium, its strati- 
graphically differentiated equivalent, and even after long experience utmost care 
must be given to their separation. If all fields of cultivation had been continuously 
irrigated till abandoned, there would be no trouble, but this was not always so. 
In the graveyard shaft, we see how an area, after having aggraded g feet under 
irrigation, was abandoned to natural forces long enough for 2.5 feet of laminated 
clays to accumulate, after which it was again cultivated during the upper 11 feet 
of growth. It took about 1o hours’ hard work to make sure how deep irrigation was 
in that shaft. No stratification can result on a cultivated area unless it be aban- 
doned long enough for natural sediments to accumulate a greater thickness than 
is disturbed by subsequent hoeing or plowing, which is 4 inches and more. At 
its base irrigation stuff is often found containing fragments of natural sediment, 
below which are remnants of the original plow or hoe trenches. A characteristic 
mass of irrigation stuff contains all sediments utterly undifferentiated except for 
the gravel and coarser grit concentrated here and there in bottoms of canals from 
time to time abandoned and buried by irrigation through new canals. It is thusa 
homogeneous mass of sandy clay. The limits of such accumulations, both ancient 
and modern, have been described. Though pre in thickness from Io to 25, 
the average appears to be 15 feet. 
Natural alluvium directly underlies irrigation sediments. Of that pene- 
trated by our shafts there appear to be three epochs of growth, differing in struc- 
ture and kind and separated by two erosion intervals as indicated in sections of 
unconformity. During the first of these, our delta appears to have been a wind- 
swept flood-plain, which through inequalities of growth from time to time gave 
rise to shifting grassy areas left isolated from alluviation for so long that wind- 
blown material accumulated on them in various degree. Such appears to have 
been the first epoch state with its resulting interbedded gravels, grit and clays 
and homogeneous loess, which were penetrated with two shafts at the North 
Kurgan and two at the South. Some change took place and the delta was divided 
by a valley, how deep we do not know. Then began our second-epoch growth of 
pure, hard, laminated clays interstratified with beds of gravel. Probably ere the 
North Kurgan was founded this new epoch had aggraded its valley flood-plain 
and refilled its delta valley to within about 8 feet of the delta’s old first-epoch 
surface, as traces of culture are found in all shafts down to this horizon, but nowhere 
below. This growth was of pure, hard clay, banded and finely laminated; blue 
when wet and yellowish when dry; it appears to bottom on a basal bed of semi- 
angular gravel, and to have ultimately risen nearly high enough to overflow the 
whole delta; that is, till the delta valley or channel was filled practically flush. 
