790 The American Naturalist [September, 
which was still fairly sound, for the bark is the last part to rot. 
Some root bark was filled with a mixture of sand and rotten 
wood. One was filled with rotten wood and a seam of sand 
shaped like a thick-backed knife blade lying lengthwise of the 
root, the back resting on the bottom, and the edge reaching to 
the top side of the hollow root bark. Since that time I have 
examined many roots along hillside exposures by the roadsides, 
and have found that the bark of the roots at a certain stage of 
decay will be filled with the same kind of earth in which the root 
lies. This would suggest that the sand or clay is carried into the 
hollow bark by insects. But I have found such root bark packed 
full of sand or clay where I thought it impossible for any insects 
large enough to handle such matter to get in, unless on leaving 
they sealed the hole so perfectly as to baffle observation. Last 
week I found one root bark about four feet long, the butt end 
filled with rotten wood and sandy clay about equally intermixed. 
The middle part was packed tight with sandy clay, and the top or 
smaller end was filled with damp rotten w^ood. In this case there 
was no noticeable insect pathway to the middle. I have dug 
trenches around old stumps and dead trees two to three feet deep to 
see what the old roots would show. Many show^ed at a distance 
of eight feet from the stump no traces of the roots whatsoever. 
In some I have found the common ants, and with them dark balls 
or lobes of mud about the shape of wheat grains, and a quarter 
to a third the size of the wheat. The teeth could plainly detect 
the grit in them. 
Suppose the trees do not reform into clay and sand, and that 
the insects carry the sand and clay into the root bark and into 
the rotten logs and stumps. They can carry none but the finest 
material. The gravel would be left behind, and this alone would 
in time work the finer material to the top. 
The crawfish is an industrious agent in wet lands in bringing up 
the lower earth to the surface. I have been examining their 
holes for the past six months, and in that time I have failed to 
find them bringing up any coarse material, though boring through 
the yellow into the glacial clay. I have so far found no gravel 
larger than bird shot in the cones which they build up about 
