yPaper G\ 



THE STRUCTURE, LITHOLOGY AND GENESIS OF THE 

 MAGNESIAN SERIES OF THE NORTHWEST- 

 ERN STATES 



[Abstract ] 

 By C. W. Hall 



An investigation of the dolomites of the upper Mississippi 

 river valley was begun more than a year ago.'^ The studies 

 to follow have been only in part carried out. This paper, present- 

 ed at the meeting of the Academy held December 6th, 1892, con- 

 tained historical matter, a discussion of the method of the study 

 pursued, and a presentation of some microscopic results. In view 

 of the writers' intention to take up again the lines of experimen- 

 tation and examination begun, and the lack of space in this Bulle- 

 tin, at the present time only a summary is given of the points 

 discussed and the results then set forth. 



But that some of the results of the field work and necessary 

 comparisons may be available, it is thought best to present a 

 key to the nomenclature of the Magnesian series. This is given 

 on the basis of the naming applied in the paper of the authors 

 just cited. The names were derived by an historical process 

 and are apparently in undisputed use at the present time. In or- 

 der that the formations may be recognized in the field under the 

 names assigned to them and that the literature may be used with- 

 out confusion, this key has been prepared. Dr. F. W. Sardeson 

 has assisted in its tabulation. 



♦The general results of the investig-ation have been published alsewhere 

 ov/ing to the unavoidable delay in the publication of this Bulletin. For these 

 results the reader is referred to "The Magnesian Series of the Northwestern 

 States," by C. ^. Hall and F. W. Sardeson, Bulletin Geol. Soc. America, Vol. 

 VI, 1895, pp. 167-198, with one plate. 



