1888 .] 
95 
[Lane. 
produced by a torsion perpendicular or parallel to said axis. There 
are yet older dikes which follow no joints. 
Turning now to unconsolidated formations, we find that the coat- 
ing of boulder clay is but scanty, and that the bed rock has 
glacial polish and striae (N. 30° W.). 1 The outjutting points, as, 
for example, Cedar Point, often show the shock and lee structure 
well, even where it could not be long preserved while the water 
was at its present level. These points show that the ice could 
not have profoundly affected the topography ; and, in view of the 
symmetrical position of the contact beds, one is tempted to sup- 
pose that the island may have been preglacially a hill preserved 
from erosion by a trap capping. 
Signs of postglacial oscillation of the sea level are seen in ele- 
vated gravels (e. g ., back of the Union Church) and in tree stumps 
below high tide mark. A number of stumps have been recently 
removed from the marsh back of Pond Beach, and they are re- 
ported from various other points. The local impression is that 
the present motion is one of submergence. The two swamps, — - 
one fresh and one salt water, — will soon be redeemed. 
The beaches range in slope from 2 : 100 to 30 : 100, and vary 
accordingly in coarseness. Lynn, Little Nahant and Pond are 
well developed barrier beaches. A curious feature is the scal- 
loped crests produced by high storms. The breaking waves act 
like a row of fountains. The breadth of these scallops is to their 
depth as 3 or 4 : 1. 
Since 1860 the east end of Lynn beach has increased much in 
breadth and height. This is due to the binding action of grass 
then planted on the blown sands. The beach is said to be losing 
on the west side. 
The deposit of blown sand extends up on to Little Nahant. 
Trenches dug in 1855 by Mr. Simmons passed through three feet of 
sand before striking a black soil which dates from the time Nahant 
was forest clad. In 1704 penalties were enacted for cutting trees. 
Part of Little Nahant is reserved for a sand pit, whence twenty 
tons were sold in 1887. 
Mr. J. H. Emerton made a few comments on the meetings of 
the Society, which led to a discussion of some of the points men- 
tioned. 
The following paper was then read : 
1 The strikes are referred to true north, and a magnetic variation of twelve degrees 
is assumed. 
