W. W. Dodge—Menevian Argillites at Braintree, Mass. 69 
mined after examination of the relation of the Weymouth and 
Hingham syenites. 
_ Braintree Syenite (L on the map).—Over a region extend- 
ing a mile and three-quarters north from the Monatoquot Valley, 
this rock occupies the spaces between the bands of slate de- 
scribed. Abutting against the steep sides of the folds, it shows 
straight and prolonged lines of junction. The two rocks may 
usually be found exposed within a few feet of each other along 
the contact line, but the actual contact is most readily observed 
at the southerly margin of the Ruggles’ Creek strip of slates. 
ear the contact, the syenite becomes compact and black or 
dark brown, porphyritic with occasional crystals imbedded in 
the ground mass but distinguishable on fresh fractures by the 
luster of the cleavage planes. This form is found on a face of 
tock bordering a narrow valley which crosses Main street east 
of Union, in Quiney (not shown on the map); the presence of 
drift-covered slates in this channel through the syenite may be 
safely inferred, although no outerop can be detected. The 
syenite is generally light or dull brown, but varies to yellow 
and to speckled gray. Near dikes of diabase, the rock is 
blackened, assuming a very different appearance from its usual 
condition. The feldspar crystals in the typical form of the 
rock are often three-eighths of an inch long, but are enclosed 
ma finer ground mass. Quartz is abundant, ut in very 
minute grains, often undistinguishable with the unaided eye. 
The hornblende is in places well crystallized and plentiful, 
usually not conspicuous, sometimes is much decomposed. 
This rock occupies but a small area in Weymouth, unless 
rocks south of the railroad are to be included with it; its 
Widest expanse is in Braintree, where it spreads from Wey- 
mouth Fore River to the valley west of Penn’s Hill. It prob- 
ably extends southward beyond the limits of the map. It never 
rises to as great elevation as does the Quincy syenite. West of 
the Old Colony Railroad, it forms the southern side of a small 
hill near the Quincy-Braintree line, west of the Granite Branch 
ilroad. Southwest of Pine Hill, it occurs on Willard street 
hear the town boundary, but northward along the West Quincy 
valley it does not appear 
toad shows the coarse syenite to be crowded with inclusions of 
diabase (?), fine grained, black, porphyritic and highly mag- 
