1881 .] 
213 
[Dodge. 
feet westward from the shaft. In both directions from the middle 
shaft, which is about 2825 feet from the east shaft, was 44 red slate ” 
much contorted. About two hundred feet westward from this 
shaft the red was replaced by 44 green slate ” with quartz, and 
intrusive rock was met with extending for 100 or 150 feet. In and 
east of the western shaft the 44 red slate ” prevails. 
North Gooseberry Island in Salem Harbor. This rocky island 
is about four hundred feet long and rises at its highest point to 
about fifty feet above low water. Its rounded top was doubtless 
shaped by glaciation, but the numerous joints which cut the rock 
in various directions have had a large effect upon its configuration, 
determining the direction and extent of sea and weather action 
upon the lower portion of its surface. Parallel joints divide the 
rock in places into slabs, vertical or inclined, sometimes not over 
half an inch in thickness, and there are three or four series which 
cross each other. 
Notwithstanding the distance to which the sea has encroached 
landward upon lower levels around these outer islands, Baker’s, 
the Gooseberries, Eagle and Lowell, they .retain a considerable 
portion of their drift covering. Yet so much of their rock bases 
is exposed that these, like most of the islands in Salem Harbor, 
and House Island perhaps best of all, afford an excellent oppor- 
tunity for studying the relation between the eruptives there shown. 
The North Gooseberry is chiefly made up of felsite. The irregu- 
lar banding of this rock is often very conspicuous on slightly weath- 
ered surfaces, curling about the numerous small pebbles enclosed. 
Upon exposed surfaces the body of the rock weathers deeply to a 
chalky white, except in the small irregular dark spots of better 
preserved material which are noticeable in all our felsite masses, 
and the small yellow feldspar crystals, sometimes well twinned, 
stand out in irregular prominence. The small black enclosed peb- 
bles are usually of a material which resists the weather better than 
the rock in which they are imbedded. There are occasional larger 
inclusions of coarse granite. In respect of the rather large lumps 
of quartz and the reddish, often well crystallized feldspar in these 
granite fragments they resemble the granite in situ on Marble- 
head neck, and that at Eagle Head, Manchester, where the granite 
is cut by felsite dikes. For careful comparison, fresher specimens 
are desirable than are naturally exposed on the island. 
