98 REPORT OF THE 



Comminuted carbonaceous matter is found in considerable 

 abundance in some of the shales of the SaltlGroup. Besides 

 this, no organic traces have been discovered. 



14. — Carboniferous Limestone. 



The best known outcrop of this formation is at Grand Rapids, 

 in Kent county, where the Grand River experiences a fall of 

 about 18 feet in the space of two miles. The rock here ex- 

 hibits gentle undulations, but the resultant dip is slightly toward 

 the northeast. It occurs in generally thin, irregular beds, 

 which are considerably broken up, and embrace frequent part- 

 ings of argillaceous and bituminous matter. In composition, 

 it is generally eminently calcareous, but in the lower portion, 

 arenaceous matter gradually gains preponderance ; and belts 

 and patches of the same material are irregularly distributed 

 through the formation. In the upper part of the exposure 

 here, is a belt, 5 feet thick, of red, ferruginous, arenaceous 

 limestone. The thickness of the formation below this is 51 

 feet, while the thickness above, at this point, is unknown, 

 though it is probably less than that below. The portion of the 

 formation below the ferruginous stratum, contains numerous 

 geodes, filled with brown and white dog-tooth spar, brown pearl 

 spar, rhombic, calcareous spar, selenite, anhydrite, aragonite, 

 pyrites, &c. 



From Grand Rapids, the formation has been traced north 

 through Ada and Cannon, in Kent county, and to the rapids of 

 the Muskegon, in Xewaygo county. South of Grand Rapids, it is 

 followed through Walker, Paris and Gaines, in Kent county, 

 to Bellevue, in Eaton county, and thence by numerous out- 

 crops to Parma, Sandstone, Spring Arbor, Summit, and Leoni, 

 in Jackson county. The S. W. J of S. E. J, sec. 13, Summit, is 

 believed to be the most southern well-characterized exposure 

 of this formation. It occurs in a quarry belonging to Michael 

 Shoemaker. The section exposed here is about 14 feet, as 

 follows : 



