
1890.] ‘St. Louis Limestone. 309 
the south, but we have not observed the underlying sandstone. 
Here the coal is found eighteen to twenty inches thick. 
The facts above cited would seem to warrant certain conclu- 
sions as to the conditions under which the limestone was de- 
posited. Its general character would seem to imply the existence 
of coral reefs fringing the shore throughout its northern extent. 
The accompanying map (Plate XI.) shows approximately the ex- 
panse of the Gulf during the St. Louis epoch. 
The probable direction of the Gulf Stream is indicated by the 
arrows. The proof of the existence of marine currents and 
clear waters along the borders in Iowa, Illinois, Indiana, and 
southward, lies in the presence at these points of extemsive beds 
of limestone. It.would séem improbable that any communica- 
tion with the ocean existed to the north and east, for had such 
existed the Gulf Stream would, doubtless, have taken that 
direction, involving clear waters and limestone deposits ; whereas, 
the arenaceous and argillaceous characters of the Lower Carbon- 
iferous of Ohio are marked. The northern extension of the Gulf 
Stream, bringing with it the warm waters of the Tropics, would 
materially affect the climate of this region, and in part explain 
the tropical conditions during the following epoch... 
The causes operating to exclude corals from tropical coasts, as 
shown by Dana,’ are: (1) cold extratropical ocean currents; (2) 
muddy, or alluvial shores, or the emptying of large rivers ; (3) 
presence of volcanic action; (4) depth of water on precipitous 
shores.. The first and third were manifestly absent. That the 
shores were not muddy is shown by the presence of the limestone 
as noted above. ? 
The general dip of the strata here is toward the south and 
west. It is very slight, but increases along the Mississippi, after 
leaving the lower line ; it changes, however, so as to bring the 
Lower Carboniferous again to the surface in the region of 
Quincy, Ill. 
There is thus afforded just such a shelving shore as would 
comport with required conditions. ; 
It is therefore not at all improbable that a line of reefs occupied 
T Manual, p. 617. 
