Upper Sihiridn in XorlhcdKfcyit lotca. — Wilson. !279 
and often striking fire with the hammer, yet being (jiiite free 
from chert nodules. 
Numerous vertical dry Joints, of short extent and roughly 
parallel, and trending generally east by south or at right an- 
gles to this, give a characteristic appearance to a weathered 
surface and cause bluffs to wear away rather rapidly from the 
splitting off' of huge vertical slabs. The top layers are very 
heavily bedded, a single layer measuring often from ten to 
twenty feet in thickness. A decided change in the fauna also 
takes place, showing a predominance of univalves and crin- 
oids. Cerionites (lactijli aides Owen, becomes more abundant. 
Ot'thoceras occurs in numerous species, as do also l^hriKimovc- 
ras, Gomphoceras ixwd Ci/rfocerffs. A small species of (Ono- 
cat'diuin, a small Spivifer, a large lieVerophon three inches in 
diameter of coil, Pisocrinns tictmniforuiis Miller, several other 
crinoids and several species of SfraiKiroJIns also occur. It is 
this upper portion of the Pentamerus beds that furnishes the 
best material for lime and it. has been very generally n^^'-'d for 
that purpose. 
At the summit of the Pentamerus lieds, there is an altrupt 
change in both the lithological and faunal features. In bluffs, 
when the two are in contact, the dividing line can generally 
be easily traced. The contact may be seen in the bluffs of the 
south fork of the Maquoketa river in Delaware county, in the 
S. W. \ sec. 24, T. 87, R. 4 ; at Flemming's mill, N. W. \ sec. 
29, T. 88, R. 4; at Hartwick in N. W. ^ sec. 30, T. 88, R. 4; 
in the bluffs of Buck creek in the south part of sec. 9, T. S7, 
R. 4; and in the N. W. \ of sec. 18, T. 87, R. 2, of l)ubu(|ue 
county. 
The overlying member has been known as the (,'oralline l)eds. 
The rock becomes softer and generally shows thinner bedding. 
The fracture is earthy, the texture is in part crystalline and 
in part coarsely granular. The system of dry joints is no 
longer seen, nor is the steel gra^^ cohu- observed on fresli frac- 
tures. The weathered surfaces are no longer covered with 
sharp projecting points and edges, nor filled with amygchihjid 
cavities, but show rounded surfaces and irregular lines of 
fracture. When these two members form the htiid surTacc. th»- 
upper part of the Pentanu^rus beds tends to assume a fhit tab- 
ular form, covered with angular blocks, whih' the Coralline 
