76 E. Andrews on the Glacial Drift of Illinois, 
inspector, and Mr. Gowan the contractor. From my own personal 
observation, and from those of the above-mentioned gentlemen, 
I derive the following facts. The tunnel is to supply the city 
with fresh water drawn from the lake at a distance of two miles 
from the shore. For this purpose a coffer dam was erected in 
the lake, two miles from the land, and within it a shaft was ex- 
eavated in the clay to the depth of about seventy-five feet below 
the surface of the water. A similar shaft was sunk at the shore 
end, and from the bottoms the workmen drifted horizontally 
until they met beneath the lake. 
at the shore end descended first through beach sand 
and then through tough clay, mostly free from boulders, and 
apparently a deposit from the lake. At the depth of about 
sixty-two feet the workmen came suddenly upon the hard gla- 
ial drift, containing glacier-scratched boulders, and in every way 
very different from the clay above it. The material appeared to 
a soft comminuted shale reduced to a clay by the same means 
which transported it from its original strata. Every cubic yard 
of it contained millions of broken and scarcely rounded little 
fragments of the shale. These were accompanied with larger 
blocks of it, mixed with glacier-scratched boulders of limestone, 
sandstone, granite, syenite, and every other kind of rock which 
exists in the regions north of us. In this and similar material 
the whole of the rest of the shaft and the entirestwo miles of 
the horizontal part of the tunnel was excavated. Some ex- 
tremely interesting facts were observed. For instance, this hard 
clay showed no trace of stratification when any particular part 
of it was inspected, yet it was so intercalated with other beds as 
