GOLDTHWAIT: SAND PLAINS OF GLACIAL LAKE SUDBURY. 293 
pavement rather suddenly stops, and the course of the brook is through - 
a narrow grassy flat, which soon broadens out into a broad swamp at 
the junction of the two headwater forks. The absence of boulders and 
blocks along the brook just up-stream may be largely or wholly due to 
the construction of a private road across the brook about 300 feet east 
of the highway, —the rocks having been collected for its construction. 
Where the northern of these two brooklets crosses the road, one finds on 
the west side of the road, going up-stream, a few bare ledges and many 
blocks, including some large boulders, and beyond these the flat swampy 
ground already mentioned as the source of the brooklets. The elevation 
at the road at this point is 165 feet (aneroid). Going down-stream from 
the road, one finds a pretty continuous boulder pavement as far as the 
broad meadow at the junction of the two brooklets, though the boulders 
are much thicker in some places than in others. There are a few bare 
ledges here, also. 
On both these brooklets the boulder pavement is a distinct and strik- 
ing feature. There is no such abundance of blocks on the slopes which 
lead away from the brooks to the north and south. The distribution is 
emphatically along the two lines of lowest ground; and the width of the 
pavement together with the general good size of the boulders seems to 
indicate that scouring much stronger than that of the present little 
stream has gone on in the past, washing the finer parts of the thin till 
cover down-stream, and leaving bare ledges and a thick pavement of 
boulders. There are no steep banks, however, enclosing the paved zone, 
such as one might expect to find. 
Down-stream from the junction, the brook follows generally a rather 
broad flat meadow ; and though boulders may once have been plentiful 
at certain points along its course, there is no longer anything like the 
boulder pavement seen up-stream. From the railroad for about 500 
feet southward along the brook, however, there are a good many boul- 
ders, possibly of some significance. Below this the valley becomes ex- 
tremely broad, flat, and swampy. These flat meadows along the brook 
are evidently aggraded parts of its valley; and they may have been 
built up by the supply of gravels and fine material from the scoured 
boulder-paved pass up-stream. 
Along the course of Stony Brook, in several places, particularly be- 
tween Kendal Green and Roberts, there are stretches of boulder pave- 
ment similar to those just described. Doubtless the brook gets its name 
from this fact. Moreover, the two large pot-holes beside the railroad 
embankment, near the northern end of Stony Brook Reservoir, may 
