HELDERBERG GROUP. 



Z1 



intricate subterranean channels which doubtless lead into the 

 lake. 



The connection of the Helderberg group with the superincum- 

 bent younger formations is in this part of the State entirely hidden 

 by drift deposits. At Blissfield, Deerfleld, and Petersburg, localities 

 which are only a short distance from the actual outcrops of the 

 Helderberg strata, in ordinary wells, dug to a depth of seventy and 

 eighty feet through drift deposits, no rock ledges have yet been 

 touched, and at Detroit, 130 feet have to be sunk through before 

 the lime rock is reached. In Prof. Winchell's geological map, pub- 

 lished in Walling's Atlas of Michigan, the southwest corner of the 

 State is represented as underlaid by the Helderberg group, through 

 a great portion of Cass and Van Buren counties and all over 

 Berrien County. This is an error; the Helderberg strata have 

 nowhere been found as the surface rock underneath the drift in 

 any of the deep borings made at Niles, Cassopolis, Michigan City, 

 or other places. 



In a deep boring lately made at the Indiana State Prison, at 

 Michigan City, the drift was found to be 170 feet deep ; below it, 

 the black shales of Ohio were struck in a thickness of ^6 feet, and, 

 finally, at a depth of 246 feet from the surface, the first limestone 

 beds of the Helderberg group were penetrated. A natural outcrop 

 of the Waverly group is north of New Buffalo, near Brown's Sta- 

 tion, not far from the Lake Shore. It is the same case south of 

 the Michigan boundary-line, on Indiana territory, where for many 

 miles no trace of a limestone formation underlying the drift can 

 be found ; it is always the subcarboniferous sand rock and its 

 intermediate shale beds which are first encountered. 



