162 
came from the west or northwest. It is interesting to observe 
that this deposit of sand is probably the only barrier between 
Little Harbor and Cohasset Harbor at this point. 
The considerable deposits of modified drift in the Beechwood 
district, south and southeast of Scituate Pond, may be regarded 
as a fragmentary development of this plain. A much lower 
plain, which, quite probably, is of marine origin, has a very 
perfect development in the district south of the Glades. It 
terminates on the east in Mitchell’s Beach and presents a very 
flat, unbroken surface, from 10 to 15 feet aboye the sea, over an 
area, nearly half a mile square. It is also scantily developed 
along the northern edge of the peneplain, in the vicinity of 
Rockland Street, and at other points; and we may reasonably 
suppose that farther inland it underlies the broad, level, and 
swampy valley of Bound Brook and its tributaries. 
Beds of clay, or the finer portion of the modified drift, appear 
to be wholly wanting above sea-level in the Nantasket and Co- 
hasset area. There can be but little doubt, however, that they 
are extensively developed under the salt marshes and in the 
drowned or marine portions of the valleys generally. The slow 
development of the salt marshes during post-glacial time 
probably commenced in every important instance with a broad, 
level expanse of the finest glacial silt or clay covered by a mod- 
erate depth of water and supporting а luxurious growth of eel 
grass. In the meshes of this dense jungle or mat of vegetation 
the detritus brought bv the tides is entrapped and slowly sinks 
to the bottom. The upper surface of the deposit is thus slowly 
'aised to the low-tide level, when the conditions become unfa- 
vorable for the growth of eel grass and the area enters upon the 
mud-flat stage. Although the main sweep of the flowing and 
ebbing tides is now through more or less definite channels or 
creeks, but little additional silt lodges on the unprotected flat 
until it has been overrun from the shore outward by higher 
forms of vegetation, when the silting-up process proceeds un- 
checked until the high-tide level is reached. A dense, firm 
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