12 
GEOLOGY: W. M. DAVIS 
Proc. N. a. S. 
normal depth in both compartments of the Tagula lagoon have been 
brought about in a region of instability and without the aid of abrasion in 
furnishing a smooth sub-lagoon platform, there is no sufficient reason for 
assuming that other flat lagoon floors of ordinary depth can have been pre- 
pared only on smooth platforms abraded at a standard depth across 
still-standing islands. It is possible that the Glacial lowering of the 
ocean surface by a moderate amount may have contributed in a manner 
that I have suggested elsewhere,^ to the production of many lagoon floors 
30 or 40 fathoms in depth ; but Glacial changes of ocean level do not seem 
otherwise to have left recognizable marks of their occurrence in the Louisi- 
ade archipelago. Crustal deformation has been dominant; and the great 
changes of shore lines thus determined appear to have been merely played 
upon by the inferred oscillations of ocean level during the Glacial period. 
This discussion is believed to show that, apart from such changes of 
ocean level as are inherently probable altho they are not well known either 
in amount or in effects, the assumptions of the Glacial-control theory are 
not applicable in the production of Tagula reef and lagoon floor ; and hence 
we may fairly conclude that these assumptions are not essential to the 
production of similar reefs and lagoon floors elsewhere. This argument, 
in which the evidence furnished by one outspoken witness for Darwin's 
theory and against the Glacial-control theory is given wide application, 
would not be valid if other witnesses were equally outspoken elsewhere 
against Darwin's theory and for the Glacial- control theory; but such is 
not the case. It must be remembered that the two main postulates of the 
Glacial-control theory, namely, long continued stability of reef foundations 
in the mid-Pacific and the abrasion of sub-lagoon platforms by the lowered 
Glacial ocean, are not based on direct evidence but are assumed because 
they are supposed to be necessary for the explanation of smooth lagoon 
floors of standard depths. Not a single example of an abraded platform 
has been discovered under recently uplifted reefs; and a good number 
of mid-Pacific islands which have a decipherable recent history are found 
not to have been long stable but to have suffered various changes of level. 
In other words, where other outspoken witnesses are found, their testi- 
mony is, like that of Tagula, for Darwin's theory of upgrowing reefs 
on subsiding foundations of whatever shape. A good number of examples 
of this kind could be adduced if space permitted. 
But although the inhibition of reef growth and the resulting abrasion 
of low-level platforms by the Glacial ocean thus appear to be excluded 
from the greater part of the coral seas, it is highly probable that reef -building 
organisms may have been weakened or killed and that abrasion of platforms 
may have taken place around islands near the margin of the coral seas; 
and at least some of those islands ought now to show plunging cliffs in 
evidence of their possession of submerged platforms ; but even there the 
