PACIFIC EXPLORATION: C SCHUCHERT 
409 
the "deeps" of the Pacific Ocean situated between 18,000 and 31,800 
feet beneath the surface occur near the continents that exist now or 
existed formerly, or that they are located on the outer or oceanic side 
of mountain chains. These, the ''foredeeps" of Suess, are striking 
tectonic features of the Kthosphere. As for the true hmits of the Pacific 
Ocean, Suess states that they are seen in the trends of long mountain 
folds. "So it is from New Zealand and New Caledonia to the borders 
of eastern Asia, to the Aleutians, and all along the western coast of 
both Americas. 
So far we have been considering the problem of crustal depressions 
essentially from the standpoint of hypothesis; now let us see what is 
actually known as to the topography of the Pacific Ocean and the geo- 
logic history of the Australasian region. An excellent summary of the 
present geography of the Pacific Ocean and the topography of its bottom 
is shown on the splendid map by Max Groll, recently published by the 
Institut fiir Meereskunde of the University of Berlin (1912). This map 
is based on Lambert's equal-area azimuthal projection, with a replotting 
of all geographic and bathymetric data ascertained up to January 1912, 
and is therefore more up-to-date and far better than any heretofore 
published. Groll states that he considered at least 15,000 soundings, 
made in all the oceans, and that yet there are many areas in the Pacific, 
hundreds of miles across, without a single one. It is therefore natural 
for him to add: "The greater part of the Pacific Ocean is still unex- 
plored. . . . One is actually frightened at the little that is yet 
known of the bottom relief of the oceans and at the few data on which 
our representation of it is based. . . . Even in so relatively well 
known an area as the East Australasian seas, there are rarely more 
than from four to six deep-sea soundings to each five-degree field." 
Our detailed knowledge of the actual configuration of the bottom of the 
Pacific is therefore seen to be very slight indeed. 
Let us now review the larger features resulting from the ancient cycles 
of aerial erosion and marine deposition through which has been deter- 
mined the paleogeography of Australasia. An analysis of this history 
since the Cambrian seems to show that at least two northeasterly trend- 
ing troughs of sedimentary accumulation began to form early in the 
Paleozoic. The western one, which may be known as the Tasman 
trough, almost wholly of Paleozoic development, is now partially ele- 
vated into the plains and mountains of eastern Australia, while the rest 
of it has sunk deep into the present sea, and with it considerable of what 
was formerly western New Zealand. The other, or eastern trough, 
which also appeared early in the Paleozoic, maintained itself after this 
