PACIFIC EXPLORATION: G. W. LITTLEHALES 
419 
mountainous walls and sharply serrated dividing ridges, while in the 
middle portion of the island there are broad expanses of rolling highlands 
which are drained by shallow channels, or short steep gulches. 
The high massive cliffs along parts of the coasts and around some 
of the largest valleys are probably due to the fact that the upper thou- 
sand feet of the ancient volcanoes consisted of superimposed sheets of 
dense lava, beneath which are breccias and tuffs which yield much more 
readily to erosion and permit the overlying massive portions to be under- 
mined. From the great depth of the sea off the coast and within the 
bays, as well as from the absence of coral reefs or of extensive sea shelves, 
it appears probable that these islands have been submerged to a con- 
siderable depth within comparatively recent times. 
IN RELATION TO THE EXTENT OF KNOWLEDGE CONCERN- 
ING THE OCEANOGRAPHY OF THE PACIFIC 
By G. W. Littlehales 
U. S. HYDROGRAPHIC OFFICE, WASHINGTON, D. C. 
Read before the Academy, April 17, 1916. Received, May 24, 1916- 
The body of water whose oceanography is under discussion is of an 
extent so vast that its area exceeds by 10,000,000 square miles the total 
land surface of the globe, and its cubical content is estimated to be 
seven-fold greater than all the land above sea-level. The indications 
are that throughout nine-tenths of its expanse the depths are greater 
than one mile, and throughout three-fourths of its expanse the depths 
are greater than two miles. It is the field of the interplay of many 
different forces exercising an important influence in terrestrial physics, 
and presents a realm of unsurpassed promise for the fruits of investi- 
gation. 
The accumulated oceanographical observations in the Pacific relate 
principally to the surface and the bottom. Even these are deficient, 
and the intermediate depths have been much less investigated. The 
materials from centuries of voyaging and from the expeditions for 
sounding the ocean sent forth since the last quarter of the nineteenth 
century, when deep-sea soundings first began to be taken in the Pacific, 
have provided information of the general distribution of barometric 
pressure and winds over this vast tract and also of the general aspects 
of surface circulation, temperature, and salinity; but the details of 
these matters have scarcely been touched. Until the tides have been 
gauged in the open ocean away from the land, it is not likely that a 
clear solution of the tidal problem will be completed. Despite the 
