Benton.] 418 [February 18, 
DESCRIPTION. 
The amygdaloid rocks under consideration lie in the eastern part — 
of the Brighton district of Boston, between North Beacon Street on 
the north, the Brookline boundary and Washington Street on the 
south, and Market Street on the west. 
They occur in the shape of two nearly continuous es (see 
map), which are very variable in direction, in height, and especially. 
in width. The general direction is about east and west, the length 
of the more northerly about three-quarters of a mile, that of the more 
southerly half a mile. The width at the head of the lane leading 
to Allston Heights is about 60 feet, while measured along Allston 
Street, itis 350 feet. These ridges of amygdaloid rise above the 
surrounding stratified rocks from 20 to 50 feet. 
The stratified rocks lie to the north and south of, and between the 
ridges of amygdaloid. Their strike is about W. N. W., and E. S. E. 
Thus it is not the same as the direction of the ridges of amygdaloid. 
The dip is about 30° to the HK. N. E. 
These rocks, though all belonging to the same geological series, 
are of two very distinct kinds : First, the fine-grained fragmental 
rocks, 7. e., the argillite and fine-grained sandstone. Second, the 
genuine conglomerate, which is composed chiefly of quartzite, felsite, 
granite, gneiss, syenite, and argillite pebbles, which are usually, at 
least, an inch or two in diameter. In this latter rock a few irregular 
layers of fine-grained sandstone are interbedded. The pebbles of 
the conglomerate are held together by a cement composed of the 
same materials as the pebbles themselves, though of course in a 
finely divided state. 
A part of the conglomerate lies to the north, and a part to the 
south of the sandstone and argillite formation, the thickness of 
these intervening rocks being eight to nine hundred feet. 
Most of the sandstone and argillite is massive, but at the head of 
the lane Jeading to Allston Heights, the argillite is fissile, and on 
Warren Street, opposite the small powder magazine, the sandstone is 
in the same condition. It also bears very perfect ripple marks, which 
show that the waves which made them came from a direction a little 
east of north. 
With regard to the relation of the amygdaloid to the argillite 
sandstone and conglomerate, in a word to the stratified rocks, it may 
be said at the outset that in every spot where overlying soil does not 
