Hartwell.] 
424 
[April 20, 
inches are unbroken. Water freezing inside has removed the 
rock from one side of it. This fragment has not been found ; it 
may be buried in the debris. 
And now comes the question as to the water which made the 
pot-hole. The streams around Pearl Hill at the present time are : 
first, Lord’s Brook, on the north, a considerable stream, flowing 
between Pearl Hill and Rattlesnake Ledges, in a valley 400 to 500 
feet lower than the top of Pearl Hill; secondly, Falulah Brook, a 
larger stream, flowing in a valley on the west, 350 feet lower 
than the summit of Pearl Hill. Between Pearl Hill and Mt. 
Vernon the valley is 500 feet lower than the summit. 
Rattlesnake Ledges are at present 800 feet high, and Mt. Ver- 
non is 760 feet, which makes Pearl Hill from two hundred to two 
hundred and fifty feet higher than any hill in the immediate 
vicinity. 
When five or six years ago this pot-hole was first found by mem- 
bers of the Agassiz Association their first and natural conclusion 
was that these streams had formed it. But this conclusion was 
abandoned after more diligent study and closer observation made 
upon the ledges. Our study convinced us that these streams 
must have flowed over Pearl Hill hundreds of thousands or mil- 
lions of years ago : for if a foot is eroded in 5,000 years, as is well 
established by experiments, simple multiplication will give the 
time it has taken to erode the present valleys. 
Observation shows that the mica schist is so soft and easily 
crumbled that this pot-hole would have been entirely eroded dur- 
ing this period of time. Observation also shows that where these 
streams flow over the mica schist, either as rapids or with a verti- 
cal descent, there are no pot-holes being eroded as fast as made, 
e. g ., Crystal Falls, on Lord’s Brook, a vertical descent of six feet ; 
Scott’s Falls, which consist of two falls ; while three fourths of a 
mile below Scott’s Falls, where the stream flows over granite in 
rapids and falls of two or three feet, we meet with several pot-holes 
and other oblong excavations. 
It becomes necessary, therefore, to look to a more recent period 
for the formation of this pot-hole. It is a well-known fact that 
streams form on the surface of a glacier and plunging into some 
crevasse form a cylindrical hole, called moulin, and the descent 
of water down this moulin would produce a pot-hole in the rock 
beneath. In this manner this pot-hole was formed, and the work 
