tS93-] 171 [Davis. 
were produced after the pebbles gained their jiresent position ; 
and to my mind, tliere is practically no question that they were 
facetted by wind-blown sand. 
The advance of facet-carving is very different in different spec- 
imens, varying presumably with time and intensity of action and 
with sti'ucture of the pebble acted on. Some pebbles are faintly 
carved, the amour t of material removed being slight and the 
facets being very small. When the facets are distinct they meet 
along a more or less sharp and straight line. Some pebbles have 
three facets, rather symmetrically disjiosed around a central apex. 
Others again have four facets, arranged in two pairs of nearly 
opposed surfaces. It is then generally the case that the faces of 
one pair are larger than those of the other ; the larger surfaces 
meeting in a main ridge line, while the smaller surfaces cut off 
the ends of this ridge. It may be supposed that the ultimate 
form of a fixed pebble, buried to a certain de])th in fine gravel, 
would be a plane surface, even with the surrounding ground ; but 
such "baselevelling" has not been observed. The action does 
not seem to be persistent enough in one position of the pebble to 
produce sucli a result. Instead of this, the long-continued action 
of the wind seems to result in an undermining of the pebble, by 
removal of the adjacent sand and gravel ; then the pebble falls 
over, generally exjaosing another side to the blast, and thus 
allowing the development of another system of facets. Some of 
the pebbles from Highland Light, where compound facetting was 
common, seem to have lost at least a fifth of their original 
volume by repeated facetting. 
Rock texture exerts a marked control of the form produced by 
the natural sand blast. The finest carving is found in the finer 
grained quartzites. The two most symmetrical specimens that I 
have seen, one found hj Mr. Woodworth on Martha's Vineyard, 
the other in my collection from South Yarmouth, are fine brown 
quartzites; both having two unequal pairs of facets, smoothly and 
sliarj)ly cut. Translucent vein quartz is not spared, although it 
is not so well carved as quartzite. Inequalities of texture not 
perceptible to the eye have been searched out in certain speci- 
mens, giving a pitted surface. A fragment of conglomerate, 
found in the railroad cut at Orleans Station, was etched so as to 
leave the contained pebbles projecting above the surface between 
them; yet it was not at all "weathered" in the sense of being 
