Benton.] 420 [February 18, 
bordered on the south side, between Harvard Avenue and Allston 
Street, by a mass of conglomerate. Here the contact is just as sharp 
as in the other localities, and an arm of the amygdaloidal rock has 
forced itself into a fissure in the conglomerate. 
The phenomena of contact which have now been cited make it 
evident that the amygdaloid is an eminently intrusive rock. In no 
case has it been found distinctly interbedded with stratified rocks. 
On the contrary, in the Pumping Station quarry it has been observed 
that the plane of contact is not coincident with the stratification, and 
jn the quarry behind the carriage factory on Allston Street, that it 
has upheaved the argillite. Hence it is probable that the igneous 
rock has not in general been driven in between the strata, but has 
rather broken through them along joint planes and fissures. 
The color of the amygdaloid is either dull purplish or dull green- 
ish gray. It is a soft rock and its powder is usually magnetic. Its 
fissures and irregular cavities are coated with quartz, chlorite 
epidote, calcite, and specular iron. 
In its amygdules occur epidote, feldspar, quartz, calcite and chlorite. 
A few of the amygdules consist wholly of epidote, some wholly of 
feldspar. More commonly, however, the outer part is feldspar, 
while the interior is occupied by epidote. The quartz usually’ *, 
occurs in small quantities in the interior of an epidote amygdule, 
and the calcite and chlorite in minute quantities in the interior of 
feldspar amygdules — both rounded and wholly irregular amygdules 
occur. 
Throughout a large part of the mass of this rock the amygdules 
exhibit no definite arrangement whatsoever, and in much of it no 
amygdules at all are tobe found. This latter is the case in parts of 
the quarry at the Pumping Station, parts of the quarry opposite the 
carriage factory on Allston Street, in the exposure at the head of the 
lane leading to Allston Heights, and in the exposure opposite the 
small powder magazine on Warren Street. In certain parts of the 
formation, however, the amygdules are disposed in a definite manner. 
One form of arrangement, the banded, consists in the grouping of 
great numbers of the amygdules into rather imperfectly defined wavy 
bands. This structure was noticed by Mr. Dodge in the quarry at 
the corner of North Beacon Street and Harvard Avenue. It is to be 
seen also in other localities. It is to be noted that the bands are not 
at all marked out by any difference in the ground mass which 
encloses the amygdules, but strictly by the occurrence and non-occur- 
