INTUonn TION TO VOL 111. PART II. 



Till. I.OUKI; *II.U,'1\N KKI'iKiTsoF Till- I I'I'KK MISSISSIPPI I'Un\- 

 IN< ORBBLATIONOI T1IK <ri; \TA WITH TIHM-: INTHK 



i INi INN Ml. 1 i . NK\\ VnUK \NI> \ \IH\N 



ANIt NIK STl! \TI, I! Al'II ir AND 

 i|STIilP,ITIiN n| THE 

 FOSSILS. 



MY N. H. WINCHEI.L AND E. O. ULRH'H. 



STHATHJRAPHK DIVISIONS OP THE LOWER SILURIAN IN MINNESOTA. 



The reader will see by reference to the table of stratigraphic designations in Part I of 

 this volume (Intnxluctiun, pp. 1 and li) a list of the special names used in the greater part 

 is volume. As, however, the use of the various designations is not entirely uniform in 

 the several chapters, and in order that the future student may have some guide in the 

 study of these format - in the field, it is necessary to present an exact definition of the 

 stratigraphy. 



The published reports of the Minnesota survey have given stratigraphic sections 

 at various places, but it has not been found possible heretofore to so adjust them as to 

 show any close successioual order, aside from that already given. The following might 

 be considered as expressing an average composition of the Trenton division of these 

 strata in southeastern Minnesota, taken in Olmsted county. It is essentially the same as 

 that published in the first annual report, and takes into account only the lithologic 

 character of the strata. 



AVERAGE SECTION OF THE TRENTON PERIOD. 



1 Loose fragment* . . 4 4 feet. 



2 Magnesian limestone, buff. . .... 30 feet. 10 Inches. 



3 Slaty and argillaceous... ; . iuebe*. 



4 Magneslan limestone, t>u(T. iif.-<-t, fl Inches. 



Shaly llmestoi ... 5 feet. 



6 Magneslan limestone, buff 20 fret. 



7 ArRillo-magnaRlao limestone with much interbedded shale (nr shaljr 



inn !,.>. Lowest seen RacepUculltes - 4 Inches 



8 Shales, with thin argillaceous sheet* of llmetton. 18 feet. 



9 Gray or earthy (bluish) limestone, with ohaly parting* 37 feet. 



-nating limestone and shale .-. Inches. 



II Gr>-n -hal.'.. 42 feet. 



i -art limestone, buff on weathirink', I'luc within, with Interbedded 



sha 22 feet. 



:7feet, 8 Inches. 



