(9;7>/// of the Locs. 
ORIGIN OF THE LOESS. 
T^HE loess, as understood in Indiana, is a thin sheet of very fine 
clay, or a sand so fine that it appears like clay, which covers 
the glacial drift. That the boulder clay, or till, here, is the work 
of an extinct glacier, is more evident the more it is studied. 
I have no more doubt of the past existence of a glacier here, 
than if I had been present when it existed, and seen it myself 
But how came the fine yellow or buff-colored, and in many 
places ash-colored, clay on top of the glacial clay. To every 
observer the first thought that will occur is that it is the sediment 
from a body of still water. Next quer>' — How did the water 
originate ? — for it must be fresh water. Well, the melting glacier 
furnished it. Ver>' well. A little more observation, and we find 
the clay at elevations rather high for a glacial pond to cover. 
Then we construct imaginary ice dams to hold the water in suffi- 
cient depth and time to make the deposits we find. Following 
our investigations southward we find the loess almost to the 
Mexican Gulf, where not only ice melts, but alligator eggs hatch 
in the sand ; yet we construct an imaginary ice dam below the 
most southern loess to account for it. Then the ice dam theory 
becomes absurd, and we cast about for another cause. The wind- 
sifted sand from the western desert next suggests the cause. But 
it too has difficulties to be reconciled and harmonized that seem 
insurmountable. 
If the clay were due to glacial lake deposits, we should expect 
the lowest valleys to contain the thickest beds of clay. But in 
my locality (Rockvillc, Ind.) the reverse is true. The highest 
land, and ridges in particular, have the thickest yellow clay, free 
from coarse sand and gravel. 
What cause or causes could produce this clay that will not be 
contradicted by well-known existing facts ? 
I suggest some causes now at work that I think could and 
did produce the clay in question. 
