302 PHYSIOGRAPHY OF CENTRAL-ASIAN DESERTS AND OASES. 
those supplying type Ib, as long as they reached the plains, could effect no more 
than a corresponding oscillation in magnitude of population. Moreover, type 
Ia was always far more in danger cf being overwhelmed by sand. 
Type II, river-bank and flood-plain oases occur along the courses of large 
streams, especially the Zerafshan. Type I is thus, to a certain degree, at the 
mercy of type II, in danger of losing part or all of its water-supply to pirating 
canals tapping the river above. Type II is relatively unaffected by climatic change 
till extreme contraction leaves it beside a dry channel. But warping of the earth’s 
crust has in some instances, such as Samarkand, seriously affected type II. Both 
type I and type II are relatively exposed to invasion by hostile people. 
Type III, or high-valley oases, are common throughout the mountains of 
Central Asia. Lying for the most part on the terraces of large valleys, they 
depend on small tributaries for water-supply. Their irrigable area being limited 
by the terraced nature of their topography, this type of oasis has in general com- 
manded an excess of water-supply and probably supported a relatively constant 
population and in their isolated conditions must have produced marked individu- 
alities of culture in a civilization left to work itself out through a long series of 
unmolested generations. 
Type IV.—Examples of both spring and well oases are still to be found far 
out on desert plains among the sand-dunes, as well as at rare intervals in the moun- 
tain wilderness. Few of them are more than nomadic camps or mere caravan 
stations on long trails of trade, and though real self-supporting centers of life in 
an otherwise lifeless region, some people would deny them the name of oasis. 
There is, however, a remarkable kind of spring oasis, really of artificial springs, 
that has been of great importance, especially in Persia and along the Persian 
frontier of the Turkoman Steppes. There it has been contrived to tap ground- 
water at the base of the mountains with a series of shafts connected by tunnels, 
leading it ever nearer the sloping surface of the plain until it is discharged at the 
oasis. The city of Askhabad, capital of Transcaspia, and many others along that 
belt, as well as farther east, are examples of such artificial spring oases. It is an 
old Persian method, doubtless introduced during the early Persian rule of this 
region, and is known as the Carice system. 
Type V.—Mr. Huntington visited lake-shore oases in Persia. Theoretically 
it is a type of great interest. We hope that future exploration may disclose the 
mound remnants of oases on now dry shores of the ancient Aralo-Caspian Sea and 
vanished lakes that lay towards the Arctic. Modern science has developed a new 
kind of lake-shore oasis, that on salt-water shores. Baku and Krasnovodsk are 
extraordinary examples of this class. All their water is distilled from the Caspian 
and there is every reason to suppose that other cities will be founded on their plan 
along the coasts of interior seas of brackish water. To what extent the ancients 
irrigated fresh-water lake-shore oases, we know not as yet; but there is no reason 
to suppose that irrigation was not carried on by them over flat areas near water- 
level in the same way in which Egypt has for many thousand years watered the 
flood-plains of the Nile. 
