GEOLOGY: W. M. DAVIS 
651 
with the physiographic history of the coastal slope, such charts cannot 
be rehed upon to present all the information that is pertinent to the 
problem under discussion. Thus if the coast of Maine were studied 
only from charts, its many embayments alternating with ragged pro- 
montories and outstanding islands, together with its small headland 
cliffs and its small bayhead deltas, might well be interpreted as indicat- 
ing the recent submergence of a hilly region that had previously been 
eroded to subdued forms : but a study of that coast on the ground soon 
discovers that it bears a discontinuous cover of marine clays up to 100 
or 200 feet above sea level; and one must therefore conclude that the 
embayments of today remain after the partial emergence of a previously 
more submerged region. 
It occasionally happens, however, that a hydrographic chart presents 
evidence which sufhces to correct a fase inference regarding recent sub- 
mergence: thus one of the Solomon islands, which has a well-embayed 
shore line, is fronted for many miles by an elevated off-shore barrier reef, 
even crested and 80 or 100 feet in height: hence although the coastal em- 
bayments show that submergence has taken place, the reef shows that 
the last change of level was an emergence, less in amount than the pre- 
vious submergence. 
In view of these examples it is evident that the chart of an embayed 
coast, outside of the coral zone and not yet examined geologically, can- 
not be trusted as indicating that the last change of ocean level was up- 
ward. Therefore the inference that there has been a general rise of 
ocean level, independent of oscillations during the Glacial period, is not 
at present well supported ; and until it is well supported, a certain amount 
of broad ocean-fioor subsidence in the coral seas, as inferred by Darwin 
from his theory of coral reefs, may be regarded as not impossible, par- 
ticularly as its effect in lowering the ocean may have been largely coun- 
teracted by equally broad ocean-floor uplifts in other regions. 
Nevertheless, it is somewhat arbitrary to assume that the broad areas 
of ocean-floor subsidence should occur chiefly in the warmer zone, where 
coral reefs could be formed, and that the areas of compensating uplift 
should be chiefly in the cooler oceans, or in those parts of the warmer 
oceans where no islands rise. Hence the supposition of local subsidence 
of volcanic islands, which usually serve as reef foundations, deserves con- 
sideration as an alternative to broad ocean-floor subsidence. This sup- 
position would be objected to by scientists of the older school, who be- 
lieved that volcanoes occupy areas of elevation. Thus Guppy said: "In 
establishing the fact of the presence of active volcanoes in regions of 
barrier reefs and atolls, I shall be removing one of the principal stand- 
