92 LOWER PENINSULA. 



a description of the general structure of the Waverly group. A 

 number of others, particularly those made in districts where no 

 superficial outcrops of rock ledges are known, are of interest, 

 and may be mentioned here. 



A drill-hole to the depth of 770 feet was made in the Court-house 

 square of Ann Arbor, whose progress I carefully watched, so that 

 I can vouch for the correctness of the record : 



Drift above coarse boulder drift, below stifi clay 

 beds mixed with pebbles and a few large 

 boulders 1 5 5 ft. 



Blue arenaceous shales interstratified with seams 



of fine-grained sandstone 1 50 " 



Black bituminous shales, evolution of hydro-car- 



buretted gas and rock oil in drops 28 " 



Gray sandstone, coarse, containing brine of 1142 

 spec, weight, leaving 19 per cent residue by 

 evaporation, which is almost pure chloride 

 of sodium 92 " 



Blue shales, with subordinate sandstone layers 



and seams of iron pyrites 100 " 



Black shales, very bituminous, with iron pyrites, 85 " 



Dark blue arenaceous shales, with iron pyrites 



and traces of fossils 22 '' 



Black bituminous shales, with iron pyrites 68 " 



Limestone, bluish-colored, with flint 70 " 



Total 770 ft 



Commenting upon this section, a parallel could be drawn be- 

 tween the upper 178 feet of shale and the Cuyahoga shales of 

 Ohio ; the lower black portion, 28 feet in thickness, would corre- 

 spond very well with the black shales on top of the Berca grit. 

 The sand rock with salt brine, 92 feet, I compare to the Berca grit 

 stones. 



The next 275 feet of shales and arenaceous layers have to be 

 taken as the equivalents of the Bedford-Cleveland-Erie shales, and 

 black shales of Ohio, and the lowest 70 feet of lime rock as repre- 

 senting the Helderberg series. In the heretofore described boring 

 at Hillsdale, the brine was found at a depth of iioo feet below the 



