310 The American Naturalist. ; [April, 
this northern shore line, just as Florida is now fringed by its 
existing representative. 
This conclusion is strengthened by the resemblance of the St. 
Louis limestone to coral rocks. Dana* describes coral rocks as: 
(1) fine-grained, compact, clinking limestone, with or without 
fossils ; (2) a compact odlite; (3) a conglomerate, mostly of corals 
and shells ; (4) a rock consisting of corals as they grew,—the 
interstices filled in with coral sand, shells, and fragments, some- 
times very loosely. By the incessant trituration of the waves 
the original features of coral rocks are toa great degree lost, and 
the odlitic and brecciated characters are the most prominent 
remaining features. 
From Le Conte? we learn that “in some places . . u 
(coral rock) is a coarse conglomerate or dreccia, Bihaca of 
fragments of all sizes cemented together; in other places itis 
made up entirely of rounded granules of coralline limestone 
(coral sand) cemented together, and forming a peculiar oôlitic 
rock. But the larger portion of the reef ground is a fine, com- 
pact limestone, made up of comminuted coralline matter (coral 
mud) cemented together. This fine coral mud is carried by 
waves and.tides into the lagoon and serves to raise its bottom ; it 
is also carried by currents and distributed widely over the neigh- 
boring sea bottoms. . . In some places it (reef rock) 
contains imbedded remains sr corals and shells, but in other parts 
it is entirely destitute of these remains.” 
The corroborative evidences of a like origin for the St. Louis 
limestone may be briefly summarized as follows: 
. In its brecciated character and uneven stratification it 
didy resembles the brecciated portions of coral rock now 
forming. In general the fragments are composed of fine-grained 
bluish-gray limestone, resembling the clinking limestone of the 
coral seas. The only coral generally distributed through it is 
the massive Lithostrotion canadense Castelnau, the remains of 
which are abundant and conspicuous. The remains of this fossil 
occur at numerous localities in Iowa, Missouri, Illinois, Indiana, 
8 Manual, p. 620. 
? Elements, p. 148. 
