THE UPLIFT OF THE TIAN SHAN. 83 
supposition of local stability within a surrounding region of depression, can to-day- 
be regarded as established for the Tian Shan. 
It may, however, be pointed out that Suess's view as to the stability of horsts 
involves extreme measures of the diminution of terrestrial volume. When the 
highland of the Bural-bas-tau is recognized as a fragment of a central Asiatic pene- 
plain, it must be recognized as having once stood not much above sea level ; and if 
8,000 or 10,000 feet out of its present total altitude of 12,000 or 13,000 feet result 
from the depression of the Siberian part of the Asiatic peneplain, then all the 
oceans and all the continents of the world must have gone down with the Siberian 
area, except for such highlands, if any, that held their own with the Bural-bas-tau. 
This seems to call upon a very large mechanism to produce a relatively small 
result. Not only so. The plateau of northern Arizona, in which the young canyon 
of the Colorado River is cut, owes its altitude, by Suess's theor)-, to the depression 
of the Great Basin region to the west of the plateau ; but this plateau is also a pene- 
plain, as Dutton has shown, hence not only the lower land to the west of it went 
down, but again all the oceans and all the continents as well, and this time the 
Bural-bas-tau with the rest — unless, indeed, the depressions of the surrounding 
regions, by which the Bural-bas-tau and the plateaus of northern Arizona were left 
in relief, both occurred at the same time. In the latter case we have onl}' to con- 
sider one of the many other more or less dissected peneplains, that of southern 
New England, for example; all of these can not possibly have been left standing by a 
single movement of depression, because their present stage of dissection is so 
unlike. It thus appears that, according to Suess's theory, the diminution of the 
the terrestrial radius at any point ma}- be measured (if we neglect the altitude above 
sea level at which peneplains are formed) by 
the sum of all the non-synchronous depressions b}- which 
the horsts of peneplains have been left in relief, 
Diinns the altitude that a peneplain (if one occurs) happens to have 
at the point of measurement. 
As said above, there may be no evidence by which the theory that leads to 
this conclusion can be absoluteh' proved or disproved, but the conclusion is a curi- 
ous one, and as long as it is ba.sed chiefly on our ignorance of the earth's internal 
mechanism, it can hardh- have general acceptance. It does not appear clearl\- from 
Suess's work whether he recognizes the necessity of this conclusion or not, for he 
does not seem to take account of the altitude that the surfaces of horsts had with 
respect to sea level before they were isolated by dislocation. Indeed, his study of 
the Face of the Earth takes relatively little account of erosion. One finds, how- 
ever, an indication of the acceptance of great changes in sea level in such sentences 
as the following: "I hope to be able to show that there is ground for correcting 
more than one general!)- accepted opinion as to the position of the le\-el of the sea 
at epochs anterior to ours" (1897, i, 782). It will be a matter of interest to see 
how far problems of this sort are treated in the final volume of Das Autlitz der 
Erde. 
