18 E. C. ANDREWS. 
features which are insequent or accidental, to the main 
topographic forms. 
The ages of all the plateaus fall within two periods, 
namely, the closing Kainozoic for the main continental range 
and the larger islands, while their smaller satellitic groups 
of islands, together with certain portions of the coast range 
of Western America, appear to be of Pleistocene age. This 
point is discussed elsewhere. 
(e) The Floor of the Pacific.—From the foregoing it is 
evident that the Pacific Basin admits readily of division 
into two related units, the one lying easterly from the 
other, and each being arranged subparallel to the main 
trend of the nearest bordering continent. The eastern mem- 
ber contains a few prominent island groups such as the 
Hawaiian, Society, Marquesas, Paumotu, Cook, Marshall, 
Hllice, and Gilbert, Groups. The floor of this portion is of 
great average depth, almost like a vast submarine plain. 
The great “‘ocean trenches” lie within its margin and their 
orientation conforms to that of the nearest surrounding 
land. Its area is 40,000,000 square miles approximately. 
As a structure it is relatively stable. This may be called 
the true Pacific. 
The western member is of less area and its floor is diver- 
sified with sea trenches, volcanic belts, and island plateaus, 
arranged in arcuate form and separated from each other by 
deep seas. The area is one of great instability when con- 
sidered in belts. This is discussed in another portion of the 
report. 
THE SOUTH WESTERN PACIFIC. 
In order to comprehend the relation between coral reef 
growths, and the structure of the Pacific, in Kainozoic time, 
it may be advisable to consider one division of the Pacific 
asa type of the whole. In this connection it would be 
