"-r i nc 



GEO, fMENT 



COLUMBIA COLLEGE 



BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL.. 3, PP. 331-368, PLS. 10-12 JUNE 23, 1892 



PALEOZOIC FORMATIONS OF SOUTHEASTERN MINNESOTA. 



• BY C. \V. HALL AND F. W. SARDESON. 



(Bnu I before the Society December 29, 1S91.) 

 CONTENTS. 



Page 



Introduction '.',:\2 



Resume" of earlier Investigations 333 



The upper Cambrian 335 



The Potsdam Sandstone 335 



The pre-Paleozoic Floor of the District 335 



The basal Conglomerates of the Potsdam 336 



Localities of the Potsdam 337 



Structural ( lharacters 337 



Lithologic Characters 338 



( 'hcmieal Composition 339 



Paleontologic ( lharacters 339 



The Magnesian Scries 340 



Subdivisions of earlier Writers 340 



Localities of the Magnesian Scries .'14.'! 



Structural Characters 34:5 



Lithologic ( lharacters 345 



Chemical Composition 347 



Paleontologic Characters 348 



The Lower Silurian 349 



( llassification of the ' rroup 349 



The Saint Peter Sandstone 350 



Localities 350 



St ructural ( lharacters 350 



Lithologic ( lharacters 351 



Paleontologic < lharacters 352 



Physical Relations 353 



The Trenton Limestones and Shales 356 



Localities 356 



Structural < lharacters 356 



Lithologic ( lharacters 356 



Chemical Composition 357 



Paleontologic < lharacters :; " ,-v 



The general Section •'• :,s 



The Buff Limestone 360 



The Blue Limestone 360 



XLV— Bum.. Gkot,, Soc. Am., Vol. 3, 1891. 331) 



