XC1V 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, 111., 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 in a good state of preservation. Salterella billingsi 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 sitbcequata, 

 Rafinesquina minnesotensis and Phylloporina sublaaxt 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. 

 In Kentucky the group is less than 50 feet thick, but in Tennessee it is as much as 100 



