142 SURFACE GEOLOGY. 
Since that time the river has been changing its course, and the overlying 
fine silt has been deposited from its floods upon the deserted river-bed. 
MopiFflep Drirr ALONG Saco RIVER AND IN THE BASIN OF OSSIPEE 
LAKE. 
The areas which are occupied by modified drift in this part of the state 
are delineated on the general geological map in the atlas; and a special 
map on Plate VI shows the extensive plains about Ossipee lake.* 
The south-eastern part of the White Mountain district is drained by 
the Saco, which has its farthest sources in Saco pond and Mt. Washing- 
ton river. The water-shed at the Crawford house, which divides this 
from the Lower Ammonoosuc river, is formed by a deposit of very coarse 
modified drift (p. 62), which was swept down into this mountain pass in 
the Champlain period. Its height is 1,900 feet above the sea; and Saco 
pond, which fills a depression in this deposit, is 20 feet lower. The small 
stream which issues from this pond passes through the White Mountain 
Notch, falling 600 feet in the first three miles, and nearly as much more 
in the next nine miles. Along this distance it flows between lofty moun- 
tains, whose sides are often precipitous walls of rock. A fine view of 
this part of its valley is afforded from the top of Mt. Willard. Far above 
rise the rugged heights of Webster and Willey, almost vertical in their 
upper part, but below bending in graceful, regular curves, composed of 
materials which have fallen from each side and form an apparently 
smoothed hollow for the highway and river. The principal superficial 
deposits along this steep portion of the river are such rocky débris which 
has crumbled from the mountains, or the equally coarse unstratified till. 
In the bed of the stream these materials have become water-worn, but 
only limited deposits of gravel and sand are found. It is worthy of note, 
that in constructing the Portland & Ogdensburg Railroad the excavations 
yielded an abundance of sandy gravel suitable for ballast. To make a 
gradual ascent, this road is built along the side of the valley; and some 
of these excavations were two or three hundred feet above the stream. 
At the west line of Bartlett the Saco is 745 feet above the sea. In the 
next eight miles to the mouth of Ellis river, it descends about 30 feet to 
* This river system is described in Vol. I, on pp. 302, 311, and 312. 
