104 
Rex T. Prider. 
p. 13). In addition there has been a considerable amount of sheai-ing aft(a- 
the formation of andalusite, which in specimen 10743 is cracked and slieared 
out into lenticles consisting mainly of sericite but carrying relicts of andalusite. 
(4) Hornblende schists (plagioclase amphibolites). 
There are several different modes of occurrence of these rocks ; — 
(1) as well defined bands (average thickness 40 feet), interbedded 
with quartzites. All have been completely recrystallised and 
variable grain features, which may indicate the original nature 
of the mass (Cooke, etc., 1931, p. 49) have been obscured. These 
bands never transgress the bedding of the associated sediments,, 
and they appear, in view of the great area ovt'r wliich they 
retain their constancy of character and liorizon, to l)e basaltic 
flows which have been folded along with the associated sediments. 
(2) as irregular shaped inclusions, usually of small areal extent, in the 
upper granitic gneiss. These are considered to be xenolithie 
bodies. 
(3) coarser-grained xenoliths in tlie lower granitic gneiss. These are 
often veined with granitic material. 
The two latter occurrences will be considered later in a section dealing 
with the xenoliths in the gneiss. 
The schistose plagioclase amifliibolites interl)edded witli the metasedi- 
mentary rocks are remarkably constant in character, consisting mainly of 
blue-green hornblende and ac'id plagioclase, with minor amounts of e})idote, 
(juartz, microcline, magnetite, s])hene and apatite. The only variants of 
this type are diopside-plagioclase amphibolites of rather rare occurrence. 
15437 is a typical example of the normal liornblende schist. It is a 
medium grained schistose rock consisting predominantly of hornblende. 
Epidote is an abundant constituent, and in hand specimen is seen to occur 
in pale yellow-green seams running ])arallel to the schistosity. 
Under the microscope the rock has a well defined schistose structure, 
the hornblende occurring in irregular shaped prisms (average 0-5-mm. long), 
in parallel alignment. Other constituents are plagioclase, microcline, epidote, 
(piartz, and sphene. 
The hornblende j^risms often carry small ])oikiloblastic inclusions of 
([uartz and felspar. The liornblende is a common blue-green variety with 
X yellow to yellow-green ; Y olive to brownish-green ; Z bluisli-green, and 
absorption X Z Y, ^ ^ 1-072 and Z/\c = 20°. 
The epidote is the pale yellow highly birefringent pistachite, usually 
confined to narrow bands parallel to the foliation. In the vicinity of epidote 
the hornblende is represented by a pale greenish bleached variety. Along 
joint cracks which are not coated with e]jidote tlie liornblende is also bleached 
— such joints traverse the hornblende crystals without dislocating them and are 
only evidenced by the jiresence of a narrow seam of more fibrous bleached 
hornblende which has the same optical orientation as the crystal traversed. 
There has clearly been some transport of material along these microsco[iical 
fractures, as seen by the occurrence of the same jiale amphibole along the 
joint plane . where it traverses ([uartz and felspar grains. 
Two varieties of felspar are present, both xenoblastic an<l slightly 
elongated parallel to tlie schistosity. Albite, which is slightly turbid with 
fine granular epidotic and fibrous sericitic alteration, is most abundant. It 
rarely shows lamellar twinning, is not zoned, and its refractive index y ^ 1-54 
indicates an albite with less than 10 per cent An. 
