194 
IDDINGS. 
these two mountains. The dikes are later eruptions through 
the breccia, and trend from the vicinity of Cache Pond in a 
north and northeast direction, some trending east. In a 
general way they radiate in the opposite direction to those 
in Electric Peak. 
The mass of Sepulchre Mountain with the body of intru¬ 
sive rocks at its west base is separated from Electric Peak 
by a profound fault that trends north and south, and has 
thrown the higher surface accumulations Of Sepulchre 
Mountain below the level of the Cretaceous strata with 
their deep-seated bodies of intruded rocks. 
'The eruptive rocks at the western edge of the Sepulchre 
Mountain mass, and directly east of the plane of faulting, 
carry large blocks of black Cretaceous shale, showing that 
they have broken up through the same strata as those 
forming Electric Peak. The effect of the faulting on the 
eruptive rocks along the east side of the fault is plainly seen. 
The rocks are shattered and fractured into small pieces, held 
together by the pulverized portion. 
Petrographical Notice of the Various Rocks. 
An investigation of all of the igneous rocks embraced with¬ 
in this small area reveals a great number of important and 
interesting facts, which it would be impossible to present at 
one time to the attention of the society. In the present 
paper it will be sufficient to notice some of the more general 
observations before describing those more intimately con¬ 
nected with the subject in hand. 
Electric Peak .—The rock-bodies forming the sheets that 
were intruded into the mass of Electric Peak before the in¬ 
trusion of the dikes consist of a group of fine grained por- 
phyrites. They are holocrystalline with slight variations in 
the grain of the groundmass. They form a group of rocks 
varying in chemical and mineralogical characters within 
certain limits. Thus they may be arranged under five differ¬ 
ent divisions, which grade into one another mineralogically, 
and mav be tabulated with reference to the phenocrysts 
