Savage and Crooks — Early Silurian Rocks. 59 



Aet. III. — Early Silurian Rocks of the Northern Penin- 

 sula of Michigan; by T. E. Savage and H. F. Crooks. 



The main body of Silurian rocks in the northern penin- 

 sula of Michigan extends in a broad arcuate belt from 

 Garden Peninsula east to Drummond Island in St. Marys 

 River, and represents a" northeastward continuation of 

 strata of corresponding age from eastern Wisconsin. 

 The Silurian rocks of northern Michigan have recently 

 been classified by Smith 1 as follows: 



Smith's subdivisions of the Silurian rocks of Northern Michigan. 



Monroe formation 



(including the Salina). 

 Upper Monroe or Detroit River series. 

 Sylvania sandstone or middle Monroe. 

 ; Silurian '" i Lower Monroe or Bass Island series. 



! "Niagara" formation. 



Engadine dolomite or upper "Niagara". 



Manistique series. 



Fiborn limestone. 



Hendricks dolomite or lower "Niagara". 



Smith's classification was made chiefly on the basis of 

 lithology, and is only in part consistent with the paleon- 

 tologic evidence which the strata afford. Recent studies 

 of the early Silurian rocks of northern Michigan by the 

 writers have brought out the fact that the two lower 

 members of the "Niagara formation" as defined by 

 Smith (the Hendricks dolomite and Fiborn limestone) in 

 this part of Michigan are equivalent in age to the May- 

 ville limestone of Wisconsin. 



The Hendricks dolomite and Fiborn limestone are 

 exposed in superposition in the Hendricks quarry and 

 test pit of the Union Carbide Company, in sec. 6, T. 44 

 N. R. 9 W. This is the type locality for the Hendricks 

 dolomite, and a detailed section of the strata exposed at 

 this place is given below : 



1 Smith, E. A., Mich. Geol. and Biol. Surv., 1915, Pub. 21, Geol. Ser. 17, 

 pp. 148 and 149. 



