The Maquoketa Shales.— James. 351 
in layers from six to twelve inches thick. Below this the 
rock is an irregularly bedded limestone, with intercalations of 
green shale extending below the bed of Fox river. It affords 
the following species of fossils : Strophomcna alternata, Orthis 
lyM; 0. bella-rugosa. Chsetetes jjetropolitanus, HeterocrinuB 
crassus, Dendrocrinus latibrachiatus, Porocrinus crassits, two 
species of JVautilus (one of which appears to be N. hercules, of 
Billings) and Tcntaculites osioegoensis.^'^^ 
In addition to these Dendrocrinus osivegoensis, and Tentacu- 
lites sterlingensis have been described from this locality. ^*^ The 
two species of Tentaculites, since recognized as forms of one, 
occur also at Cincinnati. In the county under consideration 
the group is about 71 feet thick, with a slight dip to the north- 
east. 
LaSalle count}^ is next west of Grundy. The formations are 
here principally Coal Measures. An anticlinal axis crosses 
the county east of north, and the Trenton rocks are exposed. It 
is probable that the Cincinnati rocks were once present, but they 
have been entirely eroded. In the next county to the west, 
Lee, the rocks are present to a small extent, only about 30 
feet. 
Our line next crosses the northeast corner of Whiteside 
county. Here the Cincinnati group is from 10 to 37 feet in 
thickness, this being the amount exposed at Sterling. It is 
here a hard, blue limestone, not shaly as it is generally else- 
where, and it overlies the Galena immediately. From Sterling 
Dolabra sterlingensis has been described. 
Lastly in Carroll county we reach the Mississippi river and 
find an exposure at Savannah. Here, we are told, "the lower 
part of the bed is more calcareous, and consists of thin bedded 
buff and brown limestone, some layers of which are remarkable 
for their cleavage into regular diamond shaped blocks. These 
layers are from two to four inches thick, and contain frag- 
ments of Trilobites. The upper portion of the bed at this lo- 
cality is an ash colored argillaceous shale, with thin plates of 
limestone thickly covered with fossil shells, among which are 
Orthis hjn.r, 0. occidentalis, 0. testudinaria, 0. hella-rugosa, 
Chsetetes 2')etro]politanus and fragments of jr;-?7o6?'^c.s."-' As al- 
ready noted the group here is about 80 feet in thickness. Wo 
-■^Geology of Illinois, vol. 1, p. 138, 186(). 
^'^Geology of Illinois, vol. 3, pp. 333, 343, 1868. 
