XCiV THE PALEONTOLOGY OF MINNESOTA. 
evidence of deep borings to show that it is underlaid by the St. Peter sandstone. For the 
same reason we cannot give the entire thickness of the group in Kentucky. About 325 
feet of it are exposed at High Bridge, but judging from certain fossils which occur at the 
base of the section at that point, we believe that no less than fifty feet more are covered. 
Indeed, there may be much more since the fossils in question are characteristic species of 
the Ridley limestone of Tennessee, and if the underlying limestones have as great a thick- 
ness in Kentucky as in that state, which, considering the fact that the beds equivalent to 
the Glade limestone are much thicker at High Bridge than in Tennessee, is highly 
probable, the covered portion of the group equals quite a hundred feet. The upper part 
sometimes contains much shale and is highly fossiliferous, many of the species being 
identical with those which occur in the upper beds of the group in the Minnesota region. 
Tetradium cellulosum Hall sp., perhaps the most characteristic fossil of the Birdseye in 
New York, is very abundant in this portion of the group at High Bridge and Frankfort. 
The typical Tennessee section consists of from 300 to 340 feet of alternating thin and 
heavy bedded, light blue and dove-colored compact limestones, the texture very much like 
that of the Upper Blue limestone (‘Glass rock”) at Dixon, Ill., and Mineral Point, Wis., 
and not greatly different from occasional layers found in the Lower Buff at Minneapolis. 
The lowest member (Central limestone) is thick bedded and decidedly cherty, and some of 
the layers are full of silicified fossils ina good state of preservation, Salterelia billingsit and 
Leperditia fabulites, the latter, perhaps, the most characteristic fossil of the group, occur 
in great abundance. Other fossils having an interest in this connection are Pterotheca 
alternata, Gonioceras occidentalis, Ctenodonta gibberula, Bucania emmonsi, Lophospira 
perangulata, Liospira abrupta, Solenospira prisca, and Ceraurus pleurexanthemus. 
The next -bed (Pierce limestone) is chiefly remarkable for the wonderful profusion 
of its Bryozoan fauna, some of the thin layers being completely covered with 
bifoliate forms. The ‘‘Ridley limestone” is heavily bedded again, and contains a rather 
peculiar fauna, much of it, especially among the Bryozoa, new to science. Orthis subcequata, 
Rafinesquina minnesotensis and Phylloporina sublaza are not uncommon. The ‘Glade 
limestone,” with a maximum thickness of 120 feet, consists of thin or flaggy layers and 
some shale. It is highly fossiliferous and contains many species that are characteristic of 
the group in Minnesota. 
Black River group. 
This group, though never very thick (usually from 20 to 100 feet) is still widely 
distributed, being recognizable in Canada, New York, Vermont, Pennsylvania, Tennessee, 
Kentucky and in the northwest. In Canada and the eastern states it is usually a heavy 
bedded limestone, and so it is also in Tennessee, Kentucky, Illinois and Wisconsin, but in 
Minnesota it consists almost entirely of greenish shales. The Tennessee and Kentucky 
strata which we place here have been called ‘‘Carter’s Creek limestone ” by Prof. Safford. 
Th Kentucky the group is less than 50 feet thick, but in Tennessee it is as much as 100 
