Crosby.] 370 [January 21, 
have found them, on nearly vertical, or even overhanging walls of — 
rock facing the south. ‘The ledge is divided in an east-west direc- 
tion by arather abrupt natural depression, something over five feet 
in depth; and indented pebbles have been observed on both walls of 
this. 
Another agency invoked by Mr. Wadsworth, viz.: grains of 
sand impelled .by wind and rain, is unquestionably competent to 
abrade very hard materials; and I am not disposed to deny that 
some of the effects observed at this locality may be fairly ascribed to 
its action. But here two puzzling questions arise: (1) Why, 
according to this theory, are the exposed pebbles worn away, as a 
rule, only on the north side? And (2) why are similar effects not 
observed in other localities where the same quartzite conglomerate is 
exposed under seemingly identical conditions ? 
All these considerations, however, are subordinate to the principal 
objection raised by Mr. Wadsworth, which is that the indented or 
distorted pebbles exist only on the present surface of the ledge; that 
excavation does not develop new ones; and that they are to be 
found only on those portions of the present surface which have been 
exposed for a long time to the action of the elements. In answer to 
this, I have to say, that during a recent visit to the locality, in com- 
pany with Mr. George H. Barton, my attention was directed mainly 
to a search for indented pebbles below the present surface of the 
ledge, and with such success that, although, as I have already shown, 
the paste adheres very firmly to the pebbles, so that weathering is 
usually required to develope their true forms, and it is, hence, 
natural to expect that the comparatively slight indentations attrib- 
utable to compression, will be conspicuous only on the weathered 
surface of the rock, I am able to assert with even greater positive- 
ness than before that indented pebbles do exist below the present | 
surface. 
The elongated impressions or grooves, more or less perfectly 
developed, were occasionally observed, although they seem to be 
less characteristic of the unweathered than of the weathered surfaces 
of the puddingstone; but most of the impressions were of more 
normal form. The best example of this kind was discovered by Mr. 
Barton. ‘The specimen includes three approximately equal quartzite 
pebbles. One of these, at the points where it touches the other two, 
shows two well-marked indentations which fit very neatly over, and 
have undoubtedly been produced by, the convex surfaces of the 
