CLINTON CONGLOMERATES AND WAVE MARKS. 195 
play to the waves. If the association of wave marks with these 
pebble areas be remembered, it will be readily understood that 
the forces capable of leaving these marks could lift up the 
loosened slabs of Cincinnati group and Clinton rocks, round 
them more or less, according to their constitution, size, and 
length of time of exposure, and redeposit them as pebbles over 
some other area not far distant, where the same layer might have 
been less exposed or but little affected—in other words, a little 
farther seaward. 
While, therefore, it is probable that shallow waters extended 
at various times over more or less of the Blue Grass region in 
Kentucky and Ohio, it is at no time probable that land of any 
great elevation was to be found here in Lower and Middle Silu- 
rian times. The land areas which did exist over these regions 
were always soon covered again by the sea, as far aS we can 
judge from available information. 
That land areas may have existed immediately east and south 
of the Blue Grass counties seems not improbable, but is not certain. 
The few facts known are not averse to an east and west axis of 
elevation south of these counties, and another one, running north 
and south, along the eastern border of the same. The latter 
axis seems to have been in process of elevation towards the close 
of the Lower Silurian and again during Clinton times. That this 
elevation was more marked on both sides of the Ohio river dur- 
ing Clinton times seems to be indicated by the pebbles found in 
Adams county, and that it increased here in importance by the 
fact that later the Corniferous rocks failed to appear here ; 
and that still later the Oriskany thinned out on approaching this 
lied 
The failure so far to discover pebbles derived from horizons 
decidedly below those in which they now occur imbedded, indi- 
cates that either the elevation of the land area above sea level 
was slight, or that it was of such short duration that erosion did 
not find sufficient time to produce deep river valleys or marked 
shore escarpments. In the case of a low dome-like elevation, 
the raised parts exposed to erosion would furnish the pebbles, 
