Pcirography of Mount Orford. — Dresser. 19 
enlargement of grains in crystallographic forms. The orig- 
inal grans being comparatively fresh in appearance and with- 
out any coating or iron the clastic nature of the rock is not 
easy to discern in all parts, especially as it is very compact, 
and hence the secondary silica is in relatively small amounts. 
Small fragments of a colorless mica are to be seen also, which 
are unlike any of the micas found in the accompanying ig- 
neous rocks. On the whole it is a rock that differs from the 
greywacke in conditions of deposition rather than in the 
character of the original fragmental material, and is probably 
only a phase of it.§ 
The serpentine is at this place darker in color than is usual 
in the eastern townships, presumably from the greater 
amounts of chromic iron which it contains. In the thin sec- 
tions that have been examined, the alteration of the primary 
minerals has been so nearly complete that the entire field ex- 
cept for grains of iron ore, consists eithei of dull polarizing 
serpentine or of the allied secondary form, probably bastite, 
which has a fibrous structure with the extinction parallel to 
the fibres, and polarizes in rather brilliant colors. It agrees 
in all essential respects with the serpentine of Melbourne, 
which has been described by Dr. F. D. Adams,* and of 
which mass it is practically a continuous part. 
Associated with the serpentnes are ophicalcytes and talc 
schists into which they appear to pass by rather sharp transi- 
tions. 
The ophicalcytes are mottled, light and dark green rock 
and are often quite schistose. In the thin section as well as 
in the hand specimen, the only essential constitutens are seen 
to be serpentine and calcite. The former in some places is 
in parallel bands separated by calcite, in others it forms an 
irregular network having the interstices filled with calcite. 
or it occupies irregular areas in a groundwork of calcite. 
The calcite is well crystallized and is free from specks of 
graphite or other dark colored inclusions. But it is often 
penetrated by small strings or needles or a feebly polarizing 
mineral also thought to be serpentine. The boundaries be- 
ll^ §Logan, loc. cit. 
•Op. cit. p. 19A.. 
