28 SCIENTIFIC SURVEY OF TURNER’S LAKE 
BOOM BEACH —A SEA MILL 
By JoHn M. CLARKE 
A novel expression of sea action as a geological factor is exhibited 
on Boom Beach which is a short stretch of the coast on the eastern 
shore of Isle-au-Haut, only a few rods away from the middle part of 
Turners Lake. This beach is perhaps a quarter of a mile in length 
and is bounded at the north and at the south by barricades of the rock 
pavement of the island which, though not high, exert an effective 
control of the movement of the waves. The beach is exposed to the 
full force of the Atlantic storm waves from the east. Doubtless 
the shallow waters bounding the island play over accumulations of 
large and small ice-worn glacial boulders, and this material washed 
up from the shallower depths is mixed with water-worn boulders of 
rocks indigenous to the island itself. The walled-in character of this 
sea exposure has resulted in piling up a tremendous mass of very 
heavy beach material of great width, its crest representing the high- 
est reach of the storm waves, and as a further result the slope of the 
beach is steep. As the wave action on the beach is controlled by the 
sentinel rocks north and south, a boulder once caught in this place 
is ground up and down and back and forth over the other heavy stone 
of the beach, so that such a boulder seems to be a captive forever. 
Thus the beach material is made up of various sizes of stones up to 
a number of feet in diameter, which have been put through this mill- 
ing process to a greater or less degree. The newer pieces, those 
which have been recently acquired by encroachment upon the rock 
beds of the land have only their native angles subdued, but those 
which have been longer subjected to the process are well rounded and 
approach a symmetry which is in accordance with the original shape 
of the angular blocks out of which they have beén made. The ullti- 
mate result of this grinding process, so far as it is expressed in the 
form of the boulders, is a perfect or an approximate symmetry in the 
form of an ellipsoid, or an ovoid, or a spheroid or a discoid. The 
observer is at once impressed by the very large number of these sym- 
metrically rounded blocks, all crystalline rocks and all shaped by the 
action of the sea. Nowhere has the writer seen so impressive an 
illustration of this ultimate result of the action of the sea on a beach 
of boulders. 
This exposition leads to a further consideration for somewhat 
similar occurrences which are to be seen on smaller beaches similarly 
