340 SURFACE GEOLOGY. 
In Errol, along the road to Upton, Me., we find an abundance of boulders of gran- 
itoid gneiss, which probably came from the vicinity of Wentworth pond. In Milan, 
particularly in the vicinity of Mr. Moses Hodgdon’s, we find boulders of sienite that 
must have come from Mill mountain in Stark, or from the hill immediately north; con- 
sequently the drift here could not have been more than fifteen or twenty degrees south 
of east. There are two remarkable collections of boulders in the south part of Bean’s 
Purchase, though they are derived, evidently, from ledges near where they are found. 
One of these is found a mile south from the summit of the Carter notch. The boulders 
are piled up so that they form a barrier across the valley, which is perhaps fifty feet 
higher than the depression towards the notch, in which there are two small ponds that 
have no visible outlet; but the water finds its way by an underground passage through 
the barrier, and where it issues from the rocks it forms quite a large stream. Above 
the barrier there are also many large boulders that have fallen down from the sides of 
the notch. Everywhere the boulders are angular, and their detachment from the ledges 
must have been quite recent. 
Another remarkable collection of boulders is on the east branch of the Saco, a few 
miles east of the last mentioned. Here the rock is a gneissoid granite. The boulders 
are of immense size, and are scattered over an area of half a mile in width. They are 
everywhere covered with moss; and this supports a growth of firs, which are from eight 
to ten feetin height. Travelling is extremely difficult, both on account of the trees 
and the size of boulders. After a heavy rain, far down among the rocks streams of 
water flow, the existence of which would not be suspected if they could not be heard. 
Lake Margins. The effect of the expansion of ice on our lakes, although noticeable 
in many places, is nowhere so marked as on the margin of Connecticut lake. At low 
water the rocks can be seen piled up in a wall-like structure, which on the south shore 
has a height of three or four feet, in places almost vertical. These rocks have been 
pushed a little year by year until they reached their present position, and were beyond 
the reach of ice-pressure. As the lake is now several feet above its natural level, a 
dam having been built at the outlet, if kept thus this wall will in time be removed to a 
higher level. 
