308 LAE Vi OOLINAL OR, GHOLOGN. 
of wind waves taken in connection with tidal oscillation 
in regions where the sea bottom is subjected to wave 
action at low tide. ‘ 
(3) Wave action especially facilitated by the development of 
coral reefs. 
None of these is sufficient alone to account satisfactorily for 
the brecciated limestone of the Saint Louis beds, though in 
each case favored to a certain extent by the character of the 
formation. The existence of coral reefs contemporaneous with 
the formation of this deposit, though not clearly proven, is sup- 
ported by many structural details. In lithological character 
there is a striking likeness between these deposits and those of 
modern coral reefs so well described by Dana. Professor Cham- 
berlin has described a similar character of sedimentation in the 
Niagara limestone of Wisconsin* which he ascribes to a like 
origin. The abundance of life which characterizes the Niagara 
reefs in Wisconsin, however, does not appear in the brecciated 
areas of the Saint Louis limestone in Iowa. While corals are 
present, they are not especially abundant and no coralline masses 
standing as they grew have been observed. 
The alternations sometimes seen between the brecciated and 
undistributed portions apparently favors the view that the sea 
bottom suffered an alternation between vigorous and quiet con- 
ditions during the time of its deposition. This may be ascribed 
(1) to oscillations of the earth’s crust, or (2) to tidal oscillation 
where the sea bottom lies just below low tide. 
While crustal movements were evidently in progress during 
the Saint Louis epoch, the acceptance of this view to account 
for these minor changes would imply a delicacy of adjustment 
scarcely in harmony with the character of the forces involved. 
Professor Chamberlin has called attention’ to the effect of sys- 
tematic alternation of wind waves taken in connection with tidal 
oscillation in accounting for the formation of brecciated limestone. 
In those areas where the depth of water is such that the sea bottom 
* Geology of Wisconsin, Vol. I., pp. 183-186. 
? Geology of Wisconsin, Vol. I., p. 168. 
