88 The American Geologist. August. 1903. 
Tennessee the formation attains its greatest thickness in the 
south. 
Summing the above, while the facts are not clear regarding 
the Clinton, there is a manifest possibility that a channel to the 
southward existed during the Niagara and the Lower Heldcr- 
berg periods to the east of the Ozark mountains and to the west 
of the Nashville-Cincinnati promontory which, at the most 
southerly traceable point, may have reached one hundred miles 
in width. 
Passing on to the Devonian era we find in this region in 
Missouri a limestone mentioned by Dr. Shumard at several 
points and reported to contain Spirifera arenosa. If this iden- 
tification is correct we find there an indication of an Oriskany 
channel as far as southeastern Missouri. The Upper Helder- 
berg or Corniferous outcrop also runs south from the falls and 
then westward to the Mississippi valley in Kentucky, where it 
also is lost. But it is reported again with the loss, as might be 
anticipated, of some of its distinctive features, in eastern Mis- 
souri, and again in the southeast of the same state. The Ham- 
ilton is also reported to exist in the same place and the two 
groups are scarcely distinguishable. Fossils however seem to 
warrant the admission of both. 
So far therefore as the strata can be traced, no facts forbid 
the belief in the existence of a channel to the southward where 
and when it is required by the theory of professor "Williams, 
that is to say, during the later part at least of the Silurian and 
the earlier part of the Devonian eras. The scanty exposures 
of the rocks of these eras in northeastern Alabama are their 
last outcrops to the southward, but these do not forbid their 
farther extension under cover, and it must remain for under- 
ground exploration by drilling to reveal their actual persist- 
ence along the gap between the Ozark uplift on the west and 
that of Xashville on the east. The overlap of the Cretaceous 
and Tertiary rocks from Illinois southward conceals everything 
of older date in that direction. 
Should the work of the geological surveys of the states of 
Alabama and Mississippi eventually establish the reality of the 
channel as required and as above indicated, it will be a striking 
illustration of a prophetic light cast by palaeontology on a dark- 
geological field. 
