BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 18, pp. 179-194 May is, i907 



GALENA SERIES* 



BY PEEDERICK W. SARDESON 



{Read before the Society December 29, 1906) 



CONTENTS. 



Page 



Extent 179 



Uniformity 179 



Nomenclature 183 



The Beloit formation - 184 



The Platteville limestone 186 



The formational unit 189 



Stratigraphic and paleontologic classification 190 



Extent 

 The so-called Trenton and Galena limestones of Wisconsin, Illinois, 

 Iowa, and Minnesota have long been recognized as forming a practically 

 continuous surface area, and they are so represented on geologic maps 

 (figure 1). They are nearly coextensive with the subjacent Saint Peter 

 sandstone. All three of these formations are greatly cut away by erosion 

 on their northward side and they appear to have originally extended 

 much farther than they now do in that direction. The extent of area 

 from which these formations of the Ordovician age have been denuded 

 is perhaps as great as their present surface area. This area was also 

 once doubtless covered, in part at least, by the Maquoketa shales and by 

 Silurian and Devonian formations. On the general southward side of 

 the present surface area of the so-called Trenton and Galena limestones, 

 these formations, with the overlying Maquoketa shales, extend with 

 gentle dip very far, or an indefinite distance, under formations of the 

 Silurian, of the Devonian, or of the Carboniferous, as the case may be. 



Unifoemity 



The two formations under consideration here evidently had an origi- 

 nally very wide extent ; and yet their combined thickness is perhaps never 

 much over 300 feet, nor less than 200, where they are not eroded at the 

 top. Their wide extent and their evident great uniformity of thick- 

 ness are therefore such as to indicate a very widely uniform condition at 

 the time of their deposition. The contained fossils show, of course, that 



* Manuscript received by the Secretary of the Society December 29, 1907. 

 XIV— Bull. Geol. Soc. Am., Vol. 18, 1906 (179) 



