Lower Silurian Fauna of Minnesota. 



325 



S 



I 



I 



I 



JJEVtWZAN 



h^Koff beds. so' 



Maauoketa 20' 



Lzn. 



I I 1 , 1 



I . I 1 . 1 



1 



Madurea bed sor 



Linsrtdasma bed »(y 



Gzmarella bed s<f 



Orthlsina bed 2d 



.Zysrospim bed g 



Fucoid bed 20' 



Stictopora bed aff ^§^^3 



Stictoporella icr 



Blue bed% 



Buff bed 



IS" 



Saint Peter tto- 



T7T TT- \ 



"rrn- 





wmmm 



FIGURE 8. 



Figure 8 is a diagrammatic 

 section of the Lower Silurian 

 (Ordovician) rocks of south- 

 eastern Minnesota) showing 

 the position of the beds just 

 described, their thickness 

 and their lithologic charac- 

 ters so far as practicable. 



The Saint Peter is includ- 

 ed in the Lower Silurian but 

 is partly excluded from the 

 diagram for lack of space. 



Various combinations of 

 the words Trenton etc., (on 

 the extreme left) and lime- 

 stone etc., (on the right of 

 the diagram) have been and 

 are still in use in Minnesota. 

 But such names are based 

 mainly on lithologic charac- 

 ter and conjecture and are 

 scarcely more than provi- 

 sional. The division between 

 GALENA and TRENTON is in- 

 definite. Trenton group and 

 Galena group are synonyms. 

 So also are Cincinnati group 

 and Hudson River group. 



