GHOLOGICAL CONCLUSIONS. 389 
to the presence of such an ocean continent, a set of freight 
carriers that could beat off the waves from their accustomed 
work, and push aside the ordinary oceanic currents; or else 
; a would get back all its own dirt. 
VI. ABSENCE OF FOSSILS FROM LIMESTONE STRATA. 
Absence of fossils has been mentioned as a frequent char- 
acteristic of the fine compact coral reef-rock, and also of the 
beach and drift sand-rock or odlite (pp. 153, 194). The rocks 
are formed at the sea-level, and in the midst of abundant life, 
and yet trituration by the action of the waves and winds has 
in many places reduced all to the finest. material, so that an em- 
bedded shell is seldom to be found in the beach or drift odlite, 
and rarely too in inuch of the fine-grained coral reef-rock. 
The interior basins appear to be eminently the place for 
making these non-fossiliferous limestones. This is the case in 
two widely different conditions: fist, over the portions that are 
below the coral-growing depths, which are sometimes of great 
area; and second, im lagoons that have become so small and 
shallow that corals and large shells have all disappeared, and 
the trituration is of the finest kind, producing calcareous mud ; 
such lagoons being properly in a marsh condition. These last 
appear to illustrate on a small scale the conditions under which 
many of the ancient non-fossiliferous, or sparingly fossiliferous, 
limestones were formed. 
VII. THE WIDE RANGE OF THE OLDER LIMESTONES NOT EXEMPLIFIED 
AMONG MODERN CORAL-REEF FORMATIONS. 
Coral-reefs, though they may stretch along a coast for scores 
of miles, are seldom a single mile in width at the surface ; and if 
elevated above the sea, they would stand as broad ramparts 
separated by passages mostly 20 to 200 feet deep, and often of 
