THE LOWER SILURIAN ROOKS. 



60T 



and shelving ledges of brownish, friable St. Peter's are frequent on the valley sides, and 

 isolated bluffs and towers of the same rock are to be seen a,t several places within the 

 valleys themselves. One of these towers, on the S. W. qr. of the S. E. qr. Sec. 11 

 Primrose, known as the Devil's Chimney, is circular in section, 60 feet high, 50 feet xxi, 

 diameter on the top and 40 feet at the bottom. The isolated bluff on the N. E. qr. of 

 the S. W. qr. of Sec. 28, Springdale, is 100 feet high, 100 yards in diameter at base and 

 20 on top. 



On the Wisconsin river slope the exposures and quarries, which are numerous, are 

 chiefly in the Potsdam, Mendota, Madison and Lower Magnesian. The Trenton is 

 quarried, however, on the N. E. qr. of Sec. 18, Middleton, at the top of a high bluff, 

 showing 90 feet of St. Peters (658) as represented in Fig. 51. 



Fig. 51. 



ifl^^JVE^J'ecitattJS 



S3:J'^2:E^jJ' 



J'm'J'^fSee?io«r 



?pncnfiiana r^ 



r 





':Crf:iimn-ryt riimeslotie 



Seotios Aceoss the Valley op Black Eabth Creek. 

 Vertical scale SOO feet to the inch. Horizontal scale 40O feet to tUe incti. 



The Trenton at tliis place (659, 660, 661) contains numerous casts of the following 

 fossils: Petraia corniculum, Strophomena, Cypricardites vcntricos'js Eaphistoma lenticu- 

 lare Trochonema umbilieata, MurcMsonia hicincta, M. tricarinata, Pleurotomaria Na-- 

 soni, Oncoceras pandion, and Orthoeeras anellum. The Trenton shows also in a small 

 quany at the top of the bluff on the N. W. qr. of Sec. 28, BeiTy, far away from any 

 other Trenton area. 



