186 The American Geologist. March, 1891 
mainly the operative force producing them. Microscopically the 
outlines of the pebbles do not indicate distortion or crushing ; only 
occasional cracks radiating from the indentations tell us how yield- 
ing has taken place. Nearly all of them have been derived from the 
■Carboniferous limestone and the}' therefore show a great uniformity 
as to size and outline, being well water-worn and quite broad in 
proportion to their thickness, — the longer axis corresponding to the 
bedding, although in the hand specimens the rock appears entirely 
homogeneous approximating a fine-grained marble. The present 
upper beach is made up of these pebbles simply removed from the 
Triassic beach conglomerate with but little evidence of attrition 
and orginally derived from a Carboniferous limestone ; so that at 
present there is a Quaternary conglomerate being laid down, the 
pebbles of which were eroded during Triassic time. That the 
pebbles are not being extensively water-worn by the present wave 
action is shown by the fact that the indentations are only partially 
worn away. This probably is due to the readiness with which 
they are supplied from the relatively incoherent conglomerate, 
their abundance over-taxing the power of the waves to reduce 
them so that they can be carried out to sea by the undertow, and 
permitting them to be built rapidly into a conglomerate. 
Along the line of the present upper beach there are numerous 
sea-caves. One of these deserves especial mention as it has given 
rise to a remarkable mushroom-shaped pillar, locally known as the 
<l Devil's Pulpit." This pillar, which is some eighty feet in 
hight, stands at the north end of Quaco Head and has been 
"Carved out of melaphyre by the wearing away of the Triassic sand- 
stone immediately to the west, lying unconformably on the mel- 
aphyre leaving a wall of homogeneous rock projecting to the north. 
The waves advancing from the east first formed a sea-cave at this 
point and finally perforated the mass leaving it attached to the 
main bod} - only on the landward side and at the bottom. 
Extending westerly from the extremity of Quaco Head inland 
ior a distance of about one mile and at an elevation of eighty feet 
above the present high tide level there occurs as fine an example 
of an elevated sea beach as occurs anywhere along our Atlantic 
ooast above high water mark. It is a perfect post glacial beach, 
having a gentle ascent comparable to that of the main beach in 
the harbor. Its shore line is very pronounced and is carved in 
