8o TJic American Geologist. August, i89t< 
pecially mythical seem these alleged geologic islands and their 
including seas and oceans. "Ozark and Cincinnati isles," 
"Eurasian oceans" with "Northwest passages," "Osage 
seas" and "Waverly gulfs" form very pretty geographic terms 
and can be assigned places on a map. Like Kant's "islands 
of fancy" they may be given all the characters pertaining to 
existence i7i intellectii ; but have they therefore had existence 
in ref Let us examine the evidence. 
The existence of the Cincinnati island since Silurian (Upper 
Silurian) times has been inferred: 
First and chiefly, from the present insular exposure of Or- 
dovician strata on the simimit of a broad dome or anticline. 
This exposure, a little over 13,000 square miles in extent and 
comprised within the states of Ohio, Indiana and Kentucky, 
has Cincinnati somewhat centrally placed within it. The sum- 
mit of the dome, however, is in the vicinity of Lexington, and 
"Lexington uplift" would have been a preferable name to 
"Cincinnati arch." 
Second, from indications of shallow water and shore con- 
ditions having prevailed around this area. The alleged in- 
dications are: (i) Thinning out of strata along margins of 
Silurian and Devonian, with overlap; (2) presence of conglom- 
erates and breccias in these same situations; (3) ripple mark- 
ings in the sandstones and limestones, and (4) traces of land 
vegetation.* 
In regard to (i). — It is true that Devonian and Silurian 
sediments are very thin along the margins of this area, but 
they are also even thinner under cover of the Lower Carbonif- 
erous sediments, where these go over the lower portion of the 
arch between the Kentucky and Tennessee uplifts. On the 
other hand the Waverly shows no signs of thinning along 
the margins. In the alleged instances of overlap (one is 
known where Devonian Black shale rests directly upon Ordo- 
vician limestone and shale), the proof of an interval of sub- 
aerial decay between the two deposits is wanting, or at all 
events is not conclusive. Moreover the drill also reveals these 
same "'wants" southward under cover of the Lower Carbon- 
iferous sediments. 
*On the presence of ripple marks, rain marks, mud cracks, etc., in 
the Cincinnati rocks the reader may also consult an article by N. W. 
Perry, in the American Geologist, IV., pp. Z'^^-Z7>^r 1889. [Editor.] 
