Hicks en the Qieef=(Builders. 297 
the general division of amphibole granite of Rosenbusch. 
Following Rosenbusch's classification we shall therefore have 
the following: 
( Granite (feldspar and quartz). 
Granite I Granitite. 
( Hornblende bearing granitite. 
( To be continued. ) 
THE REEF-BUILDERS. 
BY DR. LEWIS E. HICKS. 
What is the true theory of coral formations? Half a century 
ago Charles Darwin proposed the subsidence theory; half a 
dozen years ago John Murray proposed the abrasion and solution 
theory. Darwin accounts for the great thickness of the reefs 
by a sinking of the foundation as fast as the polyps built upon 
it. Murray supposes that the reef, beginning within the bathy- 
metric life-limit of the polyps, first grew up to the surface, then, 
by constant abrasion of the waves, became a factory for the 
production of coral debris^ and thus grew into deep water upon 
the talus of its own fragments, the dead landward, or inner por- 
tion (if It was an atoll), being at the same time dissolved away 
by the sea water. 
Two paths are open to us in the treatment of these theories. 
We may either set them the one over against the other in an 
antagonistic and exclusive sense, try to choose between them, 
and then try to coerce all the facts under the theory of our 
choice; or, realizing the complex nature of the phenomena and 
the possibility of some truth in both theories, we may bend our 
energies to the task of discriminating, sifting, discovering what 
kind of structures each theory will explain most satisfactorily. 
The latter path may not be the easier one, but it is certainly the 
more rational. 
At all events let us not here in America become heated par- 
tisans of either Darwin or Murray. American geologists have 
no occasion to take sides In the personal aspects of the contro- 
versy provoked by the duke of Argyll In his ''Great Lesson" 
contributed to the September number of the "Nineteenth Cen- 
