18 
IOWA ACADEMY OP SCIENCES. 
from six inches to two feet in thickness, and toward the upper 
part of the exposure the rock is made up almost wholly of the 
remains of crinoids. 
Below the first ledge noted above the beds vary from a few 
inches to a foot or more in thickness, the thinner beds prevail- 
ing near the base of the formation. Brachiopod shells con- 
stitute the major part of the material of which they are com- 
posed. 
Among the waste material of the main quarry there are 
many large blocks, eighteen inches thick, through which 
masses of chert are irregularly distributed. The position of 
the bed from which the chert- bearing blocks were obtained 
was not determined, though it is probable that it lies in the 
talus -covered space between ledges two and three of the main 
workable portion of the quarry. Whatever its position, it is a 
bed of remarkable interest, for it is in places crowded with fish 
teeth that lie embedded in the chert or among triturated brach- 
iopod shells in the calcareous portions of the layer. It looks as 
if an entire fish fauna had suffered death at once. Such gen- 
eral fatality may have been produced by any one of several 
probable causes; and, furthermore, the cause was doubtless in 
some way related to the crustal movements recorded in the 
region, and to be noted further on. Changes in oceanic cur- 
rents attended by rapid elevation or depression of temperature, 
earthquake shocks even, or concentration of sea water in an 
isolated basin, would be competent to produce the observed 
result. Whatever the cause, it was effective, and every square 
yard of sea bottom received its quota of dead fishes. 
Several genera and species are indicated amid the profusion 
of fish remains interred in this old cemetery. One of the most 
common forms is the well known Devonian type, Ptyctodus. 
Teeth of this genus are sometimes literally crowded together 
to form a sort of fish tooth conglomerate. These teeth, or tri- 
tors, vary in size and shape and in the degree of wear to which 
they were subjected before the death of their owners; but in the 
opinion of experts to whom they have been submitted, they 
probably ail belong to - the single species, Ptyctodus calceolus. 
Along with Ptyctodus are remains of one or more species of 
Devonian Placoderms, as indicated by great numbers of imper- 
fect dermal plates. The Dipnoan genus, Dipterus, is repre- 
sented by a number of the interesting wing shaped teeth char- 
acteristic of this very old but persistent type; and there are 
