26 The American Geologist. 
July. 1902 
whatever break can be found in the area, either stratigraphical 
or palaeontological. Quoting from Saftord : :;: — 
"The Lower Helderberg formation does not appear in east Tennes- 
see. The portion of the state to which it appertains is the western val- 
ley and a narrow strip of country adjoining it on the east. The areas 
and point referred to lie in a narrow strip of the country running 
across the state and contiguous to the Tennessee river on its west side, 
in which the strata of all the older formations from the Nashville 
(Hudson) to the Siliceous (Carboniferous) are suddenly beveled off. 
It will be safe to place the maximum thickness of the Lower Helder- 
berg at ioo feet. Passing eastward it grows thinner and becomes more 
or less fragmentary, until it disappears for the most part before reach- 
ing the central basin." 
These facts show that the Lower Helderberg limestone 
does not extend so far to the southward in the gulf of Appal- 
achia as does the Niagara. But at what stage in its southern 
range it runs out, the data accessible do not allow us to deter- 
mine. It is covered up in Ohio, as already explained, by the 
overlap of the Black shale in Highland and Adams counties 
and does not reappear in Kentucky, so that the only means of 
detecting its presence is by examining the records of deep bor- 
ings. These show that it passes out of Ohio with its full 
thickness of at least 500 feet, at Ironton.t from which point 
it must rapidly thin out in crossing Kentucky, or it would 
certainly reappear with the Niagara or Meniscus limestone in 
the Clinch mountain folds. 
The legitimate inference is that the Appalachian channel 
was so far contracted in the Lower Helderberg that it failed 
to reach the south line of Kentucky, and in the Corniferous 
period it fell short of what is now the south line of Ohio. 
Allowance must doubtless be made here for the loss by erosion 
during the time of elevation above the sea level. But knowl- 
edge does not qualify us to do it justly. How far the original 
limits of the formations involved have been contracted by this 
means it is impossible to say. The edges of marine strata 
are and must be eroded during a time of elevation because 
the}- are exposed while yet soft to the degrading agents, while 
the central portions of the same are usually thicker and have 
longer time to become consolidated before they emerge. But 
in the present case careful examination leads to the belief that 
* Geology of Tennessee, p. 322. 
t ideology of Ohio, vol. vi, p. 304. 
