198 W. H. SHERZER 
Between these ridges lie two broad, shallow troughs, which 
have been named from the geological beds out of which they 
have been carved, the Dundee and the Sylvania.*. The trend of 
these trough-like valleys is indicated upon the map, and also 
their extent, so far as recognized. The Dundee is the more pro- 
nounced of the two, having a breadth of two to four miles, and 
sloping downward towards Detroit at the average rate of four to 
five feet to the mile. Towards Dundee it is broader, and less 
well defined, as shown in Fig. 2. It seems to have been carved 
from the richer and softer strata of the Corniferous limestone, 
but in Wayne county it continues its direct course, while these 
strata are deflected eastward. Were it not for the deposit of 
drift, this trough would be filled with an arm of the lakes as far 
south as the southern boundary of Wayne county, standing one 
hundred feet deep at Detroit. The Sylvania trough begins in 
the west-central part of Monroe county, cutting eastward across 
the Waterlime dolomite until it strikes the outcrop of Sylvania 
sandstone, when it turns northeastward and becomes more 
accentuated in that portion which lies parallel with the Dundee 
The valley then follows the strike of the Sylvania sandstone east- 
ward and flattens out. In the northwestern part of Monroe 
county there occurs a double trough cut from the Genesee shale 
and the Hamilton shales and limestones, the latter being the 
best defined and having the same general direction and slope as 
the Dundee trough. The slope northeastward averages some 
nine feet to the mile so far as it has been followed in the well 
records. Were the drift removed, this trough would also be 
filled with water to a distance of three to four miles into Mon- 
roe county. 
In the southern half of the eastern part of this county the 
rock surface drops rather rapidly towards Lake Erie, although 
the rock strata dip in the opposite direction, thus showing that 
much material has been removed by some agencies. The drop 
averages twenty-five to thirty feet to the mile, bringing the 
rock surface about one hundred feet below the Erie level by 
* Geol. Surv., Mich., Vol. VII, Pt. I, 1900, p. 122. 
