1879. | The Formation of Cape Cod. 561 
lower than now. The occurrence of these recent marine shells up 
to one hundred feet above the sea, would disprove this conclusion 
if they lay in an undisturbed condition so as to show that they 
lived where they now are found ; instead of this, they are always 
more or less broken and worn, no two corresponding valves being 
found together; and their origin, as well as that of the lignite, 
clay boulders, and the much older fossiliferous pebbles, next to be 
described, seems to have been from pre-glacial beds which were 
formed on the floor of Massachusetts bay. These appear to have 
been eroded by the ice-sheet, lifted into its mass, and at its melt- 
ing deposited anew by the glacial rivers, their marine shells being 
thus embedded in modified drift which was accumulated above 
the sea-level The species are of northern range, such as would 
have been found living in the ocean when it was invaded by the 
onflowing ice. 
A third of a mile north from the last locality, and one half mile 
south from Highland Light, the bluff rises to a height of one 
hundred and fifty feet, and consists of sand and gravel, much 
coarser than usual, having pebbles of all sizes up to one foot in 
diameter, mostly rounded by water wearing, but a part of them 
angular, especially the larger 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 fallen down in a steep slope strown with 
pebbles. Among these are occasional fragments of a whitish 
calcareous sandstone, thickly filled with shells, which were brought 
to my notice by Mr. David F. Loring, keeper of the Highland 
Light. 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 water worn, some of them being rounded on all 
sides, indicating that their mode of transportation and deposition 
were the same; but the stratification is obscured by falling down, 
so that we do not here find these fossiliferous pebbles actually 
embedded in the drift. Before seeing any of these specimens, 
1 Marine shells occurring in the till of Scotland are similarly attributed by os 
Geikie and others, to erosion by the ice-sheet of previously existing marine 
their transportation to higher levels, so that they cannot be accepted as proof that ve 
sea stood at the height where they are now found, Geikie’s “ Great Ice Age,” 2d 
= edition, pp. 179=181. 
+ 
