378 The American Geologist. 1S ae 
Typical quartzytes are not common in this part of the 
state, and it is interesting to see such an excellent representa- 
tive of :pre-Cambrian sandstone. 
The schists and gneisses of the sedimentary formation are 
less satisfactory to deal with. They range from white to 
nearly black and, tho in typical exposures quite recognizable, 
often take on a more massive habit, and then are difficult to 
distinguish from the more gneissoid members of the igneous 
formation. As the quartzyte is considered a metamorphosed 
sandstone, so these schists and gneisses are regarded as re- 
presenting the muds and clays of the same mass of sediments. 
Similar quartzytes and schists occur some miles to the south, 
associated with crystalline limestones, the interval between 
showing the schist in abundance. 
All the facts justify a correlation of the Wellesley island 
metamorphosed sedimentary formation with the great pre- 
Cambrian sedimentary series of the Adirondack region. 
The igneous formation of the island is a granite or granite- 
eneiss, usually the latter, of rather fine grain, and red, pink, 
or light-gray color. It consists essentially of quartz, pink 
or white feldspar, (orthoclase, microcline and acid plagioc- 
lase,) hornblende and biotite, with the usual accessories. 
The igneous origin of the rock would be assumed upon 
purely internal evidence, but is established beyond a doubt 
by structural data. Eruptive contacts between the granite ana 
the schists occur on all sides. The granite contains fragments, 
of every shape and size, torn from the schists and quartzytes, 
while the latter rocks are cut in every direction by dikes and 
veins of granite ranging from yards to fractions of an inch 
in width. 
It is with the phenomena of some of the latter that this 
paper is particularly concerned, but before taking them up a 
word may be said as to the correlation of the granite. 
Like the sedimentary formation, the granite is continued 
on the mainland southward and can not be distinguishedl from: 
the great granite-gneiss formation of the western Adiron- 
dacks. The latter is an igneous complex, younger than the 
sedimentary series, made up of granite, syenyte, dioryte and 
related rocks, of various periods of intrusion, and ranging 
from \strongly foliated to wholly massive textures. While 
