94 C. Sohuch, rt — Probli m of < 'ontin< ntal Fracturing 



the "foredeeps" of Suess, are striking tectonic features of the 

 lithosphere. As for the true limits 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." 2 



Topography of the Pacific basin. — 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 topo- 

 graphy of its bottom is shown on the splendid map by Max 

 Groll, recently published by the Institut fur Aleereskunde of 

 the University of Berlin (1912). This map is based on Lam- 

 bert'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, that are 

 without a single one. It is therefore natural for him to add : 

 "The greater part of the Pacific Ocean is still unexplored. . . . 

 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 configura- 

 tion of the bottom of the Pacific is therefore seen to be very 

 slight indeed. 



Paleogeography of Australasia. 



Formation of two geosynclines (see fig. 1). — Let us now 

 review the larger features resulting from the ancient cycles of 

 aerial erosion and marine deposition through which has been 

 determined the paleogeography of Australasia. An analysis of 

 this history since the Cambrian seems to show that at least two 

 northeasterly trending troughs of sedimentary accumulation 

 began to form early in the Paleozoic. The western one, which 

 may be known as the Tasman geosyncline, almost wholly of 

 Paleozoic development, is now partially elevated into the plains 

 2 Ed. Suess, Nat. Sci., ii, 180, 1893. 



