Lansing Pleistocene Geology. — JJ'incIiell. 273 
uniform character and history of the region, viz : the creek 
occupies an inherited, pre- glacial valley, and its buried adjust- 
ment with the trunk stream must be many feet below the ' 
present floodplain, the intervening distance being the measure 
of the thickness of the total aggradation dejDosit. In the 
second place the sinking of the water of the creek every sum- 
mer, as stated by Mr. Concannon, below A in figure 2, and 
its never disappearing above A, indicates that it does not tlow 
on the rock from A to C, but on the contrary that it enters at 
A upon a mass of loose aggradation deposit into which it 
sinks at once. Again, the fact that the massive, level lime- 
stone layer that constitutes the floor of the tunnel, say twelve 
feet above the top of the creek's aggradation deposit, is cut 
away from C to A, a distance of 510 feet up the creek's val- 
ley, shows that there was a water-fall during this period of 
cutting; for this layer of limestone is underlain, at the en- 
trance to the tunnel, by more shaly and erosible beds. From 
B to A this water- fall (or rapid) must have receded, and at 
an earlier date also from C to B. Such durable layer of rock, 
lying between shales above and below, not only must have 
caused a sudden increase in the descending gradient of the 
stream, but must have been the primary cause of the excava- 
tion of a gorge in the softer shales lying below. Hence it is 
easy to infer, given the creek, and the limestone layer, that 
there is more or less of a gorge all the way from C to A, now 
filled by the aggradation deposit in question. It is not neces- 
sary to dwell on this point. It is impossible to discuss the 
age of this little creek in an impartial and thorough manner 
and exclude such early history. 
7. The statement made in No. 7 must lie explained by 
reference to some preconceived idea on the part of the author 
supplemented by a hasty and casual examination on the spot ; 
for the facts, as ascertained by the writer, are quite at variance 
from it. The thickness of materials to which professor Cham- 
berlin here refers rarely, if ever, reaches four feet. But. what- 
ever it may be as to actual thickness, it will be assunied here 
that he refers to the water-laid silt (3 in. thick) and the ma- 
terials that underlie it. In this the writer could iind no '"earthy 
debris," properly so called, no "glacial drift," no "loess" (like 
that which overlies the silt laver, or that which mantles the 
