1897.] Petrography. 221 
North Haven are squeezed normal and amygdaloidal diabases and dia- 
base tuffs. They are probably pre-Niagara in age. The fragmental 
schists in Vinal Haven are also probably pre-Niagara. They comprise 
mainly quartzitesand quartzitic slates. The basic volcanics are altered 
andesites, porphyritic diabases and andesites, and various pyroclastics. 
They were erupted in Niagara time. Following the basic lavas come 
the acid ones of Vinal Haven, consisting of various types of rhyolite, 
among the most interesting of which is a spherulitic rock containing 
spherulites of several different kinds. The commonest kind is com- 
posed of branching radiate fibers of feldspar imbedded in a granular ag- 
gregate of quartz. Flow breccias and tuffs occur intermingled with the 
massive rhyolites. The volcanic rocks are cut by dykes of quartz por- 
phyry of felsite and of diabase. The large intrusions of the southern 
portion of Vinal Haven are granites, diabases (the black granite of the 
quarrymen) and diorites. The granites are typical biotitic phases con- 
taining some hornblende. Near the contact with the diabases they are 
porphyritic. The diabase of the southern end of the island is an oli- 
vine variety, while that in the eastern part is a transition phase be- 
tween diabase and diorite. It contains brown hornblende and biotite 
in equal quantities with augite. Some phases have in addition a con- 
siderable quantity of quartz. The diorite and diabase are older than 
the granite, and both granite and basic rocks are believed to be much 
later than the voleanics. The only rocks of the two islands that show 
evidence of dynamic metamorphism are the old diabasic schists of 
North Haven. All however present many evidences of metasmatic 
alteration. Their structure remains intact, but their mineralogical 
Composition is quite different from what it was originally. The basic 
lavas are saussuritzed and their ferro-magnesian constituents are chlo- 
ritized. The glassy lavas are devitrified. 
Petrographical News.—Pockels’ argues that the magnetic polar- 
ity exhibited by many different kinds of rocks is due to conduction of 
electricity from the air. They are ‘ charged.’ 
Brauns’ describes a micro-chemical test for nitrates. A drop of the 
solution suspected of containing a nitrate is treated with a drop of 
barium chloride and warmed in the water bath. Upon cooling octahe- 
dral crystals of barium nitrate will crystallize if nitrates were originally 
present. 
€ Neues Jahrb. f. Min., etc., 1897, I, p- 66. 
"Ib, p 73. 
