112 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165 
dealt with in detail; the less prominent outcrops will be spoken of in 
a general way. The andesites are located in the townships of Chap- 
man, Mapleton, and Castle Hill, where they constitute the prominent 
ridges known as Edmunds Hill, Hobart Hill, and Castle Hill, besides 
less noticeable masses. 
EDMUNDS HILL ANDESITES. 
Edmunds Hill is situated in Chapman Township near the middle of 
the north township line, and is simply the highest part of a ridge 
running north-south for several miles. The hill itself rises some 200 
feet above the road at its base, and presents the outline of a drumlin, 
so evenly has it been graded at each end. The trees, brush, talus, and 
glacial deposits entirely conceal the formations about the base of the 
hill, and it is only after climbing half the distance to the top that the 
bare rock is found in place. In climbing the west side of the hill, 
fragments of fossiliferous sandstone were found among the andesite 
blocks, and the sandstone ledge outcrops about 100 feet below the top. 
The thickness and extent of the sandstone could not be accurately 
determined, because it was covered in so many places with heavy 
blocks and small fragments of the igneous rock which had fallen from 
above. The contact was not seen. The entire top of the hill is of 
augite-andesite. The main mass is uniform in texture, and is cut into 
large blocks by cleavage cracks. When the blocks fall down the slope 
they remain as huge masses. The south and north ends, however, and 
part of the west side, are quite different. Here the rock is split up 
into long, thin slabs b}^ a set of parallel cracks remarkabl} r uniform in 
direction and length, which retain their parallelism even when the 
rock is folded or faulted. Cross cleavages intersect these cracks every 
few feet, so that when the rock is loosened it comes out in flat slaty 
pieces one-fourth inch or so in width and several inches, or even sev- 
eral feet, in area. The whole appearance is that of thin-bedded sedi- 
mentaries which have been folded and faulted (see PL III, A). The 
general direction of these cleavage planes is N. 30° E. on the north end 
and N. 35° E. on the south end, with a dip southeast at a high angle. 
The fault planes strike N. 70° E. , and, besides cutting out the thin 
slabs at the ends of the hills, they occur all along the west side, each 
indicating a slight movement. It seems probable that the Edmunds 
Hill Ridge owes its origin, at least in part, to the formation of a fault 
block. 
The outlying knobs and hills to the east of the main mass are also 
of andesite, usually microcrystalline, but sometimes porphyritic. The 
igneous rock does not extend far to the west, but is replaced by arena- 
ceous slates, and while no precise boundaries of the formation were 
determined, the field relations suggest that the hill is the remnant of 
a lava flow over the eroded and upturned edges of sandy rocks of 
Ordovician age. 
