EVIDENCE OF SUBSIDENCE. 
313 
the Hawaian chain, the only islets not marked doubtful 
are “ Coral Eeef, Awash ” and Johnston Island. A similar 
gradation in size takes place in the Ellice, Ratack, and 
many other groups of the ocean.’ Smallness of size and 
dried lagoon basins, with occasionally a deposit of gypsum 
from evaporated sea water, are just the results which should 
be expected if the cause which had regulated the coral 
growth had been subsidence ; and gradation in it would 
result from gradation in the amount of subsidence. 
Professor Dana states that he also came to the conclu- 
sion (and this appeared to be sustained by the ‘ Tuscarora ’ 
and ‘ Challenger ’ soundings) that the belt of maximum 
subsidence in the Pacific ran from the south of Japan in 
a south-easterly direction, passing south of the Marquesas 
Group towards Easter Island. The ‘Tuscarora’ sound- 
ings indicated that transverse to the trend of the Phoenix 
Islands ( i.e . transverse to the belt of maximum sub- 
sidence), the mean submarine slopes appear to be 1 to P5 
or 1 to l - 7 (the former being nearly the maximum slopes 
of Cotopaxi, Mount Shasta, and several other volcanic 
summits of Western America), while the slopes along the 
trend are much less. This fact is more in accordance 
with a theory of extensive subsidence than of extensive 
upheaval. 
Subsidence also is indicated by the deeply indented 
shores of the Marquesas Islands, but here, probably owing 
to the boldness of the coast line, reefs are few. Tahiti on 
the contrary affords no direct proof of subsidence, and 
none of elevation, beyond that of one or two feet. But its 
broad reefs are favourable, in Professor Dana’s opinion, to 
the idea of subsidence, and he suggests that it has amounted 
to about 45 or 50 fathoms. In one island of the Navigator 
Group the indented shores seem to favour a local sub- 
sidence, but in the others there is no direct proof of 
movement in either direction. Subsidence, however, is 
