68 W. W. Dodge—Menevian Argillites at Braintree, Mass. 
variety of it which occurs on the north side of the quarry lane 
leading from Hayward’s Creek toward Penn’s Hill. 
At the trilobite quarry, south of Hayward’s Creek, the 
strike is east-west, the dip 68° south. Passing westward to 
the other side of the creek, the Braintree syenite is found at 
the surface, and this in turn disappears, farther in the same 
direction, under the Quincy syenite, while north of these the 
slates appear with the same strike, making the full width of 
the band about 1000 feet, from which the thickness may be 
estimated at 450 feet. 
The next band, more than an eighth of a mile northward, 
lying between Quincy avenue and South street, is more than 
400 feet wide, and over half a mile long. The strata of this 
fold have high dip; their strike is substantially east and west. 
Half a mile east-southeast of Quincy railroad station are 450 
feet of slates dipping southward, and with strike N. 75° 
° E. beneath the surface, would lie 
extending for nearly half a mile, 500 feet wide, with Braintree 
syenite immediately south of them. At both of these places 
the slate has frequent large oval cavities partially filled with 
epidote, which are sometimes irregularly scattered, sometimes 
distributed along lines of decoloration (perbaps also intrusion) 
parallel to the stratification plane. Diabase is found with the 
slate in Quincy (east side of Union street), where its presence, 
securing immunity from glaciation, accounts for the abundant 
exposures of the various rocks to the southward. ‘The rocks, 
Penn’s Hill. The North Weymouth beds lie in the direction 
of the strike of the fossiliferous beds at Hayward’s Creek, and 
would naturally be regarded as the eastward continuation of 
these. Their own strike at North street is N. 80° W., and 
although nearer Fore River it is west, their westward extension 
may be parallel to Washington street. It is not improbable, 
however, that the northern surface limit of the most northerly 
area of Braintree syenite is determined by glaciation rather 
than by the actual extension of the rock, and that the slates 
north of this have, except locally, the more common east an 
west direction. 
here seems to be no reason to doubt that the argillites of all 
these folds are of the same age. Their maximuin thickness 
appears to be not far from 500 feet. The relation of the argil- 
lites and the Hingham conglomerates can be more safely deter- 
