392 THE ILLINOIS GLACIAL LOBE. 



THICKNESS OF DRIFT. 



These ridges occupy a region iu which the drift deposits are very 

 thick, but it is probable that the drift deposited at the time of their forma- 

 tion is mainly confined to the ridges, with only a thin sheet on the plain 

 which separates them and the plain between the Covert Ridge and the lake. 

 The relief of the ridges probably represents approximately the thickness of 

 the drift deposited at this stage. The following list of borings which have 

 struck rock indicate that throughout much of this district the rock surface 

 lies considerably below the surface of Lake Michigan: 



At Hammond, in Lake County, Indiana, the distillery well penetrated 

 110 feet of drift, reaching a level 95 feet below the surface of Lake 

 Michigan before entering rock. 



At Owen's brick yards, in Hobart, Indiana, rock was entered at 150 

 feet, at a level 100 feet below the surface of Lake Michigan. 



The Blair artesian well, in the northeast part of Porter Count}', entered 

 rock at 240 feet, at a level 220 feet below the surface of Lake Michigan. 



At the northern Indiana penitentiary, near Michigan City, Indiana, 

 rock was entered at 172 feet, at a level 156 feet below Lake Michigan. 

 A gas boring in Michigan City reached a level 230 feet below the lake 

 before entering rock. 



At New Buffalo, Michigan, a boring penetrated 212 feet of drift, enter- 

 ing rock at 192 feet below the level of Lake Michigan. 1 



At New Troy, Michigan, a well is reported to have struck rock at only 

 65 feet, or at a level but 20 feet below Lake Michigan. A well near New 

 Troy, in sec, 30, T. 7 S., R. 19 W., is reported to have entered shale at a 

 depth of 90 feet and a level about 20 feet below the lake. 



At Sawyer Station, Michigan, Mr. Rough sunk a well which entered 

 rock at a depth of 123 feet and a level 56 feet below Lake Michigan. 



At Bridgman, Michigan, a well at the box factor)- entered rock at 140 

 feet, at a level 78 feet below Lake Michigan. 



At the basket factory in St. Joseph, Michigan, rock is entered at about 

 123 feet below Lake Michigan and at a similar level in a well at the Park 

 Hotel. The gas well at Benton Harbor entered rock at 124 feet below the 

 level of the lake. 



' Geol. of Indiana, 1873, p. 431. 



