HISTORICAL SKETCH. xlvii 



The second paper compares, bed for bed, the different parts of the Lower Silurian in 

 Minnesota with their supposed equivalents in Wisconsin, and divides the same in Minne- 

 sota as follows, naming some of the characteristic fossils of each. 



The Cincinnati group comprises: 



Wykoff beds, limestone 50 feet 



Maquoketa beds, limestone and shale 20 " 



The Galena embraces: 



Maclurea bed, limestone 50 " 



Lingulasma bed, limestone 20 " 



Camarella bed, limestone 30 " 



Orthisina bed, shale 20 " 



In the Trenton are placed the following: 



Zygospira bed, shale 8 



Pucoid bed, shale 20 



Stictopora bed, shale 30 



Stictoporella bed, shale 10 



Blue bed, limestone 12 



Buff bed, limestone 15 



Total 285 " 



This substantially divides the strata covered by the investigations of this volume into 

 three limestones separated by two epochs of shale. The Devonian is said to lie uncon- 

 formably on the Wykoff limestone . 



The third paper describes a number of new forms and presents a table showing the 

 stratigraphic range of all the species found by the author in the Lower Silurian; the same 

 subdivisions are used as above. These three papers constitute an important addition to 

 the stratigraphic paleontology of the Minnesota Lower Silurian. 



0. W. Hall and F. W. Sardeson. 



1892. Paleozoic formations of southeastern Minnesota, by C. W. HALL and F. W. SAR- 

 DESON. Bulletin of the Geological Society of America, vol. in, pp. 331-368, June 23, 1892, 



This paper repeats the classification and the paleontological results expressed in the 

 foregoing papers of Mr. Sardeson. It embraces also various structural and petrographical 

 information relating to the Upper Cambrian and the Lower Silurian in Minnesota. 



In speaking of the paleontological characters of the St. Peter sandstone some fossils 

 lately found near St. Paul are named, which in the opinion of the authors show the Lower 

 Silurian age of this sandstone. They are: 



Murchisonia gracilis Hall. 

 Murchisonia perangulata Hall. 

 Two new species of Modiolopsis. 

 Undetermined species of Telllnomya. 

 Undetermined species of Endoceras. 



THE REPORTS OF THE MINNESOTA SURVEY. 



1872-1892. Several of the annual reports of the Minnesota survey have dealt with 

 the strata and the fossils of the Lower Silurian, viz: 



