82 TJie Amaican Geologist. August, ii>98 
axis of the anticline and a little to the eastward of it is the 
"Kentucky River fault." This fault exhibits a maximum 
displacement of about 300 feet. It shows every evidence of 
being contemporaneous in formation with the uplift. Only 
Ordovician strata are now involved in it. Upon the theory 
of the late Ordovician or early Silurian age of the Cincinnati 
anticlinal island, this is all the strata that could have been in- 
volved in it, and the fault must therefore have been a surface 
phenomenon in Silurian times, presenting an escarpment to 
the east of 300 feet. The Kentucky river strikes this fault at 
Boonesboro and turns southwestward, crossing and recrossing 
the line of the fault eight miles before it finally crosses to the 
west at Camp Nelson. If this fault were formed antecedent 
to the river and the country has suffered so little denudation 
as would be indicated by the bare removal of this three hun- 
dred foot escarpment, it must in all probability have presented 
a considerable face even after the Kentucky river was estab- 
lished, and we have the strange phenomenon of a river run- 
ning up a slope of an anticline and deliberately attacking and 
breaching an escarpment nine times. If the river were ante- 
cedent to the fault or if the latter were not originally a marked 
surface phenomenon, we can understand how the river might 
adjust itself to the changing conditions as it found them, pre- 
serving a record of this in its diversion to the southwest. 
Second. — The indications of a vast amount of denudation 
in this region renders it probable — almost certain — that the 
arch was formerly covered by all the latter formations up to 
and including the Carboniferous. Traces of the former pre- 
sence of these formations are abundant. The Lexington 
Limestone (Trenton formation of the Kentucky survey re- 
ports) forms the surface rock on the summit of this dome over 
1,060 square miles. It has here a thickness of 200 feet, with 
the top 975 feet above the sea. It constitutes by weathering the 
typical blue grass soil. Tongues and outliers of the Cincinnati 
(Hudson of the Kentucky survey reports) prove that this for- 
mation once covered the whole Trenton blue grass area. On 
the very summit of the arch a faulted outlier (a wedge-block 
between two faults) preserves middle Cincinnati (Hudson) 
sandstone. The fault escarpments have been entirely re- 
moved. 
