ICE WORK IN SOUTHEASTERN MICHIGAN 197 
Rock topography.— Through- 
out the main region under discus- 
sion the bed rock consists, in 
descending order, of Genesee 
shale (St. Clair), Hamilton shale 
and limestone (Traverse), Cor- 
niferous limestone (Dundee), 
and Waterlime dolomite with an 
intercalated bed of very friable 
sandstone (Sylvania). The strata 
have a general northeast and 
southwest strike and dip to the 
northwest at an angle of two to 
five degrees. An embossment 
of rock, ten to twenty miles broad, 
underlies the greater part of Mon- 
roe county, and extends north- 
eastward into Wayne, gradually 
dropping toward Detroit. The 
highest elevation attained by this 
bed rock is about 680 feet, at the 
head of Ottawa Lake, southwest- 
ern Monroe county. Upon the 
broad crest of this embossment 
are carried three minor ridges, 
one in the eastern part, another in 
the central,and the third toward 
the western part of the two coun- 
ties. These ridges seem to cor- 
respond with the strike of the lay- 
ers, and presumably consist of 
somewhat harder rock. They fur- 
nish the various natural and arti- 
ficial exposures now available for 
study, the most northern of which 
is at Trenton (see Fig. 2). 
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