788 The American Naturalist. [September. 
than the surface yellow day? This too is consistent with the 
thicker clay on the higher lands where vegetation first existed. 
But chemistry teaches that it is impossible that trees, roots, 
leaves, and the flesh and blood of animals, birds and insects 
should turn to clay or sand. Then the more wonderful the facts 
I submit herein. For the time being I shall treat the facts 
according to their appearances, for appearances point so strongly, 
that the investigator on the field, shovel in hand, requires a con- 
stant effort to doubt them. But I remember too that the 
appearance of the surface of the earth is flat. 
But here is a large erratic glacial bowlder on top of very recent 
creation. Why was it not covered by this recent creation? Ah, 
I see ; once on top by any accident at the end of the glacial 
epoch, the subsequent freezing and thawing would keep it there. 
The freeze takes place at the outer edges first, forms an air-tight 
box, and in expanding lifts the bowlder, thus forcing a vacuum 
under it, which is filled with water by suction, which water is next 
frozen, causing still another lift and expansion. This second lift 
raises the bowlder above the first outside frozen support, causing a 
crevice. The succeeding thaw, which takes place first at the 
outer edges, forms a thin slush which fills the crevices, acting thus 
as props or supporting or staying wedges. Sometimes a 
bowlder will be so covered with a drift of leaves or the fall of a 
tree that the freeze does not get enough under to lift it. Then it 
ceases to climb on top as the building goes on, and it will in time 
be found in the midst of the surface yellow clay as we have often 
seen jthem. 
Then again we find stray glacial gravel interspersed among the 
gravelless clay. Query — How came it there? The crows may 
have carried it and dropped the pebbles, as they do to-day ; or 
the squirrel and other similar habited animals in digging through 
the leaves after fallen nuts may have kept them scratched up to 
the surface for a long time, and then by chance they were over- 
taken by a leaf drift, and remained where we find them to-day, 
in the midst of the surface clay. Also, animals burrowing in the 
gravel would carry the gravel up from their holes and leave it on 
the surface. 
