ICE WORK IN SOUTHEASTERN MICHIGAN BOY 
so will be these toy affairs, for which differential ice action can 
scarcely be invoked! Pebbles embedded in the ice do not come 
into action suddenly and do not thus gouge the rock. Hard 
pebbles from about which the clay may have been washed and 
upon which the ice during its slight readvance may have settled 
could hardly have been thus forced into the limestone by the 
plastic ice. If the ice was not plastic then what became of these 
pebbles, there being no evidence of their having been crushed in 
the basins or troughs? These are some of the difficulties the 
writer has encountered in trying to arrive at an explanation of 
the phenomena. 
Early Wisconsin.— Previous to the glaciation just described 
there was a general and more vigorous movement south-south- 
west across this region, which must be referred to the early 
Wisconsin stage. On the north side of the quarry there are to 
be found ‘lee and stoss”” phenomena, “‘ knobs and trails”? and 
the above described effect upon the distal side of previously 
formed furrows. The general effect upon the rock surface was 
very largely obliterated by the late Wisconsin ice and the striz 
and gouges are preserved mainly in furrows made by this earlier 
sheet itself or in those already in existence when it invaded this 
region. The mean of twenty-one observations taken on all sides of 
the quarry gives for the general direction of movement S. 30.8° 
W., with a rage of 19.5° (S. 20.5° W.to S. 40° W.). This direc- 
tion makes an angle of 120° with that of the late Wisconsin in 
this vicinity, it is manifestly older and there is evidence that it 
acted more vigorously, was presumably more massive and capa- 
ble of reaching further south. 
lowan ?— A still earlier set of striz than that above described 
is to be seen in certain rock-basins and troughs partially exposed 
at the northeastern part of the quarry, and in some of less size 
at the southeastern part. At the time of a visit to the quarry 
five years ago afew readings were made in a trough which has 
been since partially removed, these readings averaging S.64° W. 
During the past fall fifteen additional readings gave a mean of 
S68 On We swith acrance Ob) 1235.0 (S17 O555 . Wetolsn 73s VN). 
