200 WORET A SELLE LAL Ke 
DRIFT OF THE REGION. 
Till A mantle of typical Wisconsin till covers the rock, 
except over the limited areas where the rocks are naturally 
exposed, or where it has been artificially removed about the 
quarries. This would average from forty to fifty feet in thick- 
ness in Monroe county, and perhaps seventy-five to eighty feet 
in Wayne. Inthe Traverse trough the drift is 140 to 150 feet 
thick, somewhat less beneath Detroit and Windsor. Westward 
toward the Defiance moraine the till thickens in Washtenaw 
county to two hundred feet west of Ypsilanti. We have no 
evidence of more than one sheet of this till. Occasional well 
records in southern Wayne and northern Monroe counties speak 
of seams of a black, combustible substance, generally referred 
to as ‘coal,’ but no continuous layer of black soil or peat 
exists. ‘‘Hard-pan”’ is not infrequently mentioned, and it is 
not improbable that isolated patches of early Wisconsin or pre- 
Wisconsin till may have escaped the late Wisconsin ice. At 
present writing, the twelve-foot shaft of the Michigan Rock Salt 
Co. has just penetrated seventy-one feet of till at Ecorse, just 
south of Detroit. This section gives four feet of muck; two 
feet of mucky clay; four feet of a mottled lake clay, yellow, 
brown, and blue in color, with shells, but no pebbles; and some 
seventy feet of soft, bluish-drab till, carrying pebbles and 
bowlders. The only break in this sheet of till was found at a 
depth of thirty feet, where a six to eight-inch layer of gravel 
was encountered. In certain regions the till may be discolored 
to a depth of several feet, the maximum being fourteen, as 
reported at Dundee. Generally, blue clay can be found quite 
near the surface. Bowlders are distributed sparingly over the 
two counties, lying upon the surface or embedded in the deposits 
from the glacial lakes. Huge masses of limestone, of the 
nature of “transported ledges,” have been found in the till and 
mistaken for outcrops of bed rock.* 
*WINCHELL, “Some Indications of a Northward Transportation of Drift Mate- 
rials in the Lower Peninsula of Michigan,” Am. Jour. Sci., 2d ser., Vol. XL, pp. 331- 
38. Also Geol. Surv. Mich., Vol. VII, Pt. I, p. 22. 
