164 General Notes. [February, 
probably arises from the fact that such are” seldom seen 2” situ 
north of the southern limit of the drift, having been removed 
from their places of origin during the ice age. It may not be un- 
interesting to those geologists whose studies are in the field of 
surface deposits to know of a convenient locality where such 
boulders are even in the process of being made, as doubtless very 
many of the erratics, especially those of larger size, were thus 
produced before their subsequent transportation, as pointed out 
by Dr. Sterry Hunt and others. 
At several localities in the District of Columbia, boulders of 
various sizes can be seen, which to the superficial observer may be 
taken for drift masses, as in my own case upon earlier visits to 
exposed for a depth of forty or fifty feet or more. Much of the 
gneiss rock is disintegrated, but contains unaltered masses which 
have resisted the atmospheric decay. The rock is often poor in 
feldspar. In some places it is hornblendic. Some of the gneiss 
upon weathering exhibits a schistose structure, yet much is re- 
markably compact, but traversed by numerous jointed planes, 
extending in all directions. As the weathering proceeds from the 
jointed planes it leaves solid masses of every possible shape, from 
those with only the more exposed upper solid angles rounded off, 
through various forms where all the angles are removed, but with 
flat sides remaining, representing the original joint planes, to 
masses which are almost perfectly spheroidal, though often show- 
ing a banded structure. Internally some of the smaller boulders 
are more or less decayed, others are perfectly compact, but in 
digging them out there may be seen surrounding them concentric 
- zones, marking not concretionary structure but the progress ot 
Upon the sloping top of the hills there are large sized boulders ; 
with their angles and faces more or less rounded, and although 
standing two, three or four feet above the grass-covered soil of 
decomposed gneiss, yet their under portions, upon examination, 
are found to be connected with the solid masses beneath. Thus 
we find in every stage of production excellent examples of the 
genesis of large “boulders of decomposition ”— boulders not 
distinguishable from very many of those which have, been trans- 
ee oN 
