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planes. Somewhat prominent joint-planes hade S. about 45°. 
Dy taking advantage of the lowest stage of the tide, it is pos- 
sible to add a little to the meagre knowledge of the geology of 
northern Hull afforded by the ledges just described. The 
Toddy Rocks, one fourth mile north of Telegraph Hill, were 
visited with a boat at low tide and found to be ledges of a 
bright green slate, with very perfect cleavage, which strikes 
№. 75° E. and hades to the north 0°—5°. The true bedding 
lines dip north at low angles, 10°-20°. Some thin and very 
hard compact layers of a gray color are probably intrusive 
(trap). This outcrop is evidently essentially similar to that 
south of Thornbush Hill; and slate of the same general char- 
acter is the most abundant rock in the drumlins and on the 
stony beaches of northern Hull. Bowlders of conglomerate 
and sandstone are so rare as to indicate that they have prob- 
ably been transported by ice; and we hazard little in reg: rding 
the part of Hull between Point Allerton and Windmill Point 
as having a continuous foundation or axis of slate. One and 
one half miles east of Point Allerton, and fully a mile south of 
the line of strike of the slate at the foot of Thornbush Hill, is 
Harding's Ledge. This is partly bare at low tide, exposing a 
hard grayish and greenish sandstone varying to a fine conglom- 
erate. It is an undoubted ledge ; and these rocks are probably on 
the line of the anticline of Hough’s Neck, which we may sup- 
pose to extend by the north side of Grape Island, Bumpkin 
Island, Strawberry Hill, and Strawberry Ledge to Harding’s 
Ledge. It is manifestly impossible, without going beyond the 
limits of Hull, to reach any definite conclusion concerning the 
relations of the slate beds to the conglomerate and melaphyr 
series. It is probably safe to assume, however, that here, as 
elsewhere in the Boston Basin, these soft and arenaceous slates 
normally overlie the conglomerate, the latter appearing, as a 
rule, only along denuded antielines. According to this view, 
not only northern Hull, but the entire peninsula north of 
Atlantic Hill, is underlain chiefly by slate; and to account for 
