332 77^6 Cincinnati Bocks. — Perry. 
He also says : "If these inequalities of surface are due to 
wave action of an\' sort, it is impossible to see wh}' the action 
should be limited entirely to the finest limestone beds of the 
series, while the soft shales which could so easily register any 
movement of the waters never exhibit the slightest indications 
of such agencies.'" 
The wave-marks at Ludlow, Ky., which liave crests some 
six or seven inches high and whose distance apart is three or 
more feet, are in limestone not of the finest structure, but on 
the contrary of very coarse structure. They are almost wholly 
made up of the fragments of crinoid stems and other equally 
coarse debris. This is also the case in many other localities 
visited where waves of similar size were found, though they do 
also occur in the finer limestones, as in some of the horizons 
in the Little Four Mile creek. 
His statement that the soft shales "could so easily register 
any of the movements of the water'' does not seem to me to 
be in accordance with good reasoning. It would seem rather 
that they could register the movements of the water only in 
exceptional cases, such as in very small and shallow pools 
where the agitation of the water could not become sufficient 
to keep the very light earthy matter in suspension. Where 
the waves were larger this material (the shale) would if pre- 
viously deposited be taken into suspension by the agitation of 
the water, and if in suspension would remain so until the 
movement of the water completely subsided when it would be 
slowly deposited in a regular layer, covering up the heavier 
limestone which had kept a record of the movement. Such 
Avould seem more plausible and entirely in accordance with 
the facts as we have found them. In the shales such mark- 
ings could only be made and jireserved under a concurrence 
of exceptional circumstances, and I therefore look upon their 
discovery as a fortunate and important one, instead of one to 
bo expected. 
His suggestion that concretionary action was probably the 
cause of these so-called wave-marks, must, I think, from the 
evidence of the waves themselves, fall to the ground. 
While some of these markings are found in a very fine- 
grained and homogeneous limestone under conditions where 
concretionary action might be looked for, yet the majority, 
