366 HALL AND SARDESON PALEOZOIC FORMATIONS OF MINNESOTA. 



20 feet. The entire thickness is not known, since at no single exposure 

 have both top and bottom layers been seen; but it is estimated at 30 or 

 more feet. The limestone layers contain trilobite and Endoceras m remains 

 in good preservation. The shales contain the remains of a few species of 

 molluscoidea in great numbers. 



Lithologic Characters. — The crystalline condition of portions of these 

 shales has just been mentioned. The typical hand specimens show a 

 strikingly mottled stone, which displays varying shades of light brown, 

 faint yellow and white (see plate 12, figure 6). In texture it is much 

 finer than the average Lower Silurian limestones or somewhat massive 

 shales. It is not thoroughly crystalline, but is made up of partially 

 crystalline material, with immense numbers of minute fossils, apparently 

 of many and diverse species. 



Paleontologic Characters. — The following fossils have been identified: 



Leptsena prsecosis, Sardeson. Strophomena alternata (/), Hall. 



Orthis corpulenta, Sardeson. S. unicostata, M. and W. 



Streptorhynchus trilobatum, Owen. 



The Wykoff Beds: Localities. — These beds are seen in Fillmore comity, 

 between Wykoff and Spring Valley, and at Spring Valley in exposures 

 along the Chicago, Milwaukee and Saint Paul railway. In the town of 

 Bristol, near Granger village, there are several small exposures. 



Structural Characters. — The Cincinnati limestone of Minnesota under 

 the above designation, one suggested by the prominent characters it dis- 

 plays near the village of Wykoff, in the western part of Fillmore county, 

 is rather heavily bedded. It is only 20 to 25 feet thick along the railway 

 named, but it becomes 70 feet or more in thickness only 15 miles further 

 southward along the Iowa line, in Bristol. It is easily eroded, and a 

 shaly appearance is the first and most conspicuous result of this action. 

 In fact the term " shale," which has sometimes been applied to this 

 scries of strata, by no means expresses its lithologic or structural condi- 

 tion when fresh and unaltered material is seen. 



Paleontologic Characters. — The following fossils are known : 



Leptsena recedens, Sardeson. S. wisconsensis, Whitfield. 



L. saxea, Sardeson. Strophomena alternata {?), Hall. 



Orthis corpulenta, Sardeson. S. unicostata, M. and W. 



0. hanhdkensis, McChesney. Bellerophon bilobatus, Sowerby. 



0. ma.crior, Sardeson. Murchisonia gracilis, Hall. 



O.petrse, Sardeson. Pterinea demissa. Hall. 



0. subquadrata, Hall. Tellinomya lepida, Sardeson. 



Rhynchonella capax, Conrad. Modiolopsis modiolaris, Hall. 



Streptorhynchus trilobatum, Owen. 



