4 SCIENTIFIC SURVEY OF TURNER’S LAKE 
are obviously of a later term, as among these are stratified quartzites 
still retaining the cross-bedding of the original beach-sand composing 
them. The island rocks have been thoroughly glaciated and ice 
scratches are to be seen from the shore line to the summit of the 
hills, wherever the composition of the rocks has enabled them to 
hold against the weathering. This is not often as most of the 
rocks yield easily to decomposition and it is chiefly on the diabase 
dikes and hard hornblendic schists that such scratches are retained. 
The level of the island above the sea has changed in comparatively 
late times. The “Thoroughfare” which separates Isle-au-Haut 
from Kimball Island at the northwest, is at full tide open to craft 
of slight draft, but at low water it is completely choked by broad 
mussel banks. An extension of these banks has been found well 
inland along the filled rock trough at the north, lying at a depth that 
indicates considerable elevation above the present sea line. Evi- 
dences of such slight upward movements are to be seen in the gen- 
erally rounded contour of the rock shores at the east and west. At 
the south the steeper cliffs, many of which are conspicuous, seem to 
owe their origin less to any change in the elevation of the land than 
to the attacks from the open Atlantic against a rock wall weakened 
by cross folds and joints. 
The ice sheet and its consequent debris are doubtless responsible 
for much obstructed drainage which has produced swampy areas 
over the uplands, and to that agency we must ascribe the apparent 
overdeepening or scouring of the rock valley at the east, in which 
arises the extraordinary lake which it is the purpose of this publica- 
tion to describe ;— Turner’s Lake; the name stands for one of the 
oldest families on the island, and to those who are wont to resort to 
the place on summer days it is still reminiscent of the times when 
the self-reliant islanders, depending upon the resources of the fishing, 
leaned less heavily than today upon contacts with the world outside. 
It is not quite certain to the writer whether this lake lies in a fault 
valley parallel with the crystalline rock folds, or is a cleaned-out syn- 
clinal or a glacial trough. Its shore is bounded by low rock outcrops, 
but they are not sufficiently different in inclination or composition to 
determine this point. However, the following are the salient intro- 
ductory descriptive features of this little lacustrine basin: It is 1.2 
miles long, 1/10 mile wide, straight, and almost due north and 
south; its north end is 700 yards from the Atlantic Ocean at the 
east, the boundary between lake and sea being a rock ledge 20 to 
Ao feet high; at the south it is 150 yards from the sea into which 
— 
