jSgj.j 169 [Davis. 
were found along the base of the cliff ; sometimes apparently in 
place, but then held in large masses of gravel which had slipped 
down from the top of the cliff. 
If it be postulated that these buried facetted pebbles have been 
carved by wind-blown sand, as they certainly seem to be, then it 
must be concluded that at least those beds of stratified sands and 
gravels which contain facetted pebbles were deposited by sub- 
aerial processes, and not by marine processes below sea level. 
First, as to the postulate that the pebbles are wind-carved. 
Leaving the general discussion of this subject to the paper by Mr. 
Woodworth, above mentioned, 1 may briefly consider the alter- 
naXive explanations ; namely, the production of facets by splitting 
on joint faces ; and by action nnder water, instead of under air. 
Professor Shaler describes and illustrates the facetted pebbles 
of Nantucket under the name of "split pebbles," in bis paper on 
the Geology of that island (Bull. 53, U. S geol. surv., 1889, 23- 
26, and plate 10). He compares them to the chipped stones 
found by Dr. Abbott in the Trenton gravels, but shows that 
while they in a measure resemble artificially-cut stones, yet they 
must be regarded as natural i^roducts. He does not consider 
their production by wind action, but ascribes them to splitting on 
joint faces during a recession of the ice sheet by which they were 
brought part way on their journey from their source ; after which 
they were again carried forward during a later advance of the 
ice. They are described as being "found in relatively great 
iibundance in all the pebble-drift sections at Nantucket. At 
Sankaty Head they occur at a depth of 25 feet or so at the crest 
of the cliff, in positions which seem to indicate that they could 
not have slipped down from the surface." Although regai'ded as 
having been deposited with the rest of the sands and gravels of 
the beds in which they occur, the attitude of the facetted face of 
tlie pebbles in the gravel beds is not specified. 
While recognizing this process as a natural one and of presum- 
ably frequent occurrence, it does not seem to have been effective 
in producing facetted jjebbles of the kind here described, for 
these forms are not known in unaltered glacial till. It cannot 
have been the process by which the characteristic facetted stones 
of Cape Cod were produced, as it certainly was not by this 
process that they were so carefully laid, edges up, in the beds 
of gravel and sand. The edged stones are not .weathered or 
