1879. ] 1 37 (Crosby. 
I spent two or three hours in hunting for these pebbles, obtaining five 
pieces which were six inches to a foot in diameter, with several others 
of smaller size. One of the large pieces which had a good exposure 
of the enclosed shells was presented to the Boston Society of Natural 
History. In October I again visited the locality, making a longer 
search than before and finding about a dozen pieces of the shelly 
rock, most of them less than eight inches in diameter, which were 
also presented to the Society and placed in your hands for determin- 
ation. The cliff from which these pebbles were obtained is on the 
east side of Cape Cod, in Truro, one-half mile south of the Highland 
Light. This bank is some twenty feet higher than that on which the 
licht-house is built, being about one hundred and fifty feet above the 
sea. It consists of sand and gravel, the pebbles being of all sizes up 
to a foot in diameter, mostly rounded by water wearing, but a part of 
them angular, especially the large pieces, some of which may be two 
feet long. The foot of the cliffs here is guarded from the waves by 
several rods of sea-sand covered by beach-grass, so that the gravel 
and sand have failen down in a steep slope strewn with pebbles, 
among which these pieces of shelly rock are found. They occur 
rarely for twenty or thirty rods along the face of the cliff, at all 
heights up to one hundred and twenty-five feet, being most abundant 
between seventy-five and one hundred feet above the sea. Like the 
other pebbles, most of these pieces are more or less waterworn, some 
of them being rounded on all sides, indicating that their modes of 
transportation and deposition were the same; but the stratification 
of this cliff is obscured by falling down, so that we do not here find 
these fossiliferous pebbles actually imbedded in an undisturbed drift 
deposit. 
Before gathering any of these specimens, however, I had found a 
fragment of similar shelly rock four miles further south, in a layer of 
gravel five feet thick overlaid and underlaid by regular strata of sand. 
This gravel was at a height of thirty feet above the sea, with one 
hundred feet of sand and gravel above it, evidently occupying its 
original place in the extensive deposits of modified drift which form 
this part of Cape Cod. Examination along the whole line of cliffs 
which extends more than fifteen miles on the east side of this 
peninsula, from Nauset Lights to High Head in the north part of 
Truro, composed entirely of gravel and sand with local deposits of 
clay, failed to discover any other fragments of this rock, except that 
two bits of it were found in a freshly exposed section of sand and 
