Relations of the Igneous Rocks— Crosby. yi 
granite in the quartz porphyry and minor apophyses of the 
latter in the former. 
On this hill, also, the quartz porphyry dike is cut by a 
four-foot dike of compact and purple felsite, and gives off 
an oblique branch 20 feet wide, traceable for a thousand 
feet, and cut by another felsite dike 10 to 15 feet wide. 
The phenocrysts of the branch dike are relatively small 
and inconspicuous, and comparable in size with those of 
the contact zone ; while this contrast between the main 
dike and its branch proves that in neither case can the 
phenocrysts be regarded as antedating the intrusion of the 
magma. On the other hand, the lithologic resemblance 
of the branch dike to the quartz porphyry phase of the con- 
tact zone must be regarded as a mere coincidence, since we 
have to do in the one case with the earlier phase of the bath- 
olite, and in the other with relatively late intrusions cutting, 
as we shall see, all of the sedentary zones of the batholite 
from the normal granite to the quartz porphyry. 
Southeastward, the main dike is traceable across the 
reservation boundary and nearly to the Boston-Hyde park 
line, where it is seen to cut the quartz porphyry of the 
contact zone and the enclosed masses of Cambrian slate. 
In the opposite direction from Bearberry hill, across the 
drift-floored valley of Turtle pond and beyond Washington 
street, in the large Cottage avenue quarry in normal gran- 
ite, capped by fine granite, and exactly where the great dike 
of quartz porphyry might be expected to reappear, we find 
instead, and with the same trend, a dike of profusely por- 
phyritic granite porphyry, 30 to 50 feet wide. With 
aphanitic and firmly welded margins, it cuts, clearly and 
unmistakably, both the normal and the fine granite ; and 
it is, in turn, cut squarely across by a small dike (2 to 4 
feet) of felsite in which the fluxion structure parallel with 
the irregular walls is beautifully developed. Apparently, 
there is no reason to doubt that this intrusive granite por- 
phyry which Dr. Bascom regards as essentially identical in 
composition with the normal granite, is also simply a more 
crystalline phase of the intrusive quartz porphyry', the two 
rocks being part of one and the same continuous dike ; and 
facts vet to be noted abundantlv confirm this conclusion: 
