198 
MR. 0. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
and traces of orthoclase, being a little muscovite and grains of zircon. In an old 
Hmyaudwin, near Momeit-road pass, fragments of a similar rock are found, passing 
into a quartz-schist by the increase of muscovite, and containing also grains of 
graphite. 
At Nyoungouk an aplite is found, containing a felspar with a structure like that 
of anorthoclase (cryptoperthite), some quartz, a little plagioclase and a blue 
tourmaline (indicolite), showing a beautiful zoned structure, and in places passing 
into pink tourmaline (rubellite). See Plate 6, fig. 8. 
At Mandalay Hill the aplite, which contains both orthoclase and plagioclase 
felspar with quartz, is sometimes changed to a greenish colour by the develojnnent of 
ferromagnesian silicates (epidote and chlorite ?) and at other times acquires a pinkish 
tint by the development of scales of hematite from the included magnetite. This 
rock also contains corundum (sapphire). 
When these finer-grained (aplite) rocks contain, as they frequently do, garnets 
(almandine) they assume all the characters of ordinary granulites or leptynites 
(“ Weissstein ” of the Germans). A rock of this class is found at Yenee River Falls, 
near Mogok, in which the pale-red garnets exhibit anomalous double refraction ; in 
this rock too, the beautiful green chrome-mica (fuchsite) is found. A few grains of 
brown biotite are not rare in some of these aplites and granulites, which thus 
graduate into the ordinary biotite-gneisses of the district. A very good example of 
one of these rocks constituting a transition between the aplites and the ordinary 
biotite gneisses is found between Mogok and Momeit. 
In their general characters these foliated pegmatites and aplites, intercalated 
among the biotite-gneisses, present a very close analogy with the massive pegmatites 
and aplites that occur as the so-called “ contemporaneous” or “ segregation” veins in 
so many of the eruptive granites. 
There are numerous examples of rocks, transitional in character, between these acid 
types and the normal gneisses of the district. Thus, at Letnytaung Mountain, we 
find a rock rich in plagioclase,—which forms large crystals, just as in the pegmatites,— 
with much brown mica and a dark brown hornblende. This hornblende is remark¬ 
able for its intense pleochroism, the scheme of pleocliroism and absorption being as 
follows : — 
9. Yellowish-brown. 
it Very dark greenish-brown. 
f. Intensely dark brownish-green. 
c = fe > a. 
There is a very striking resemblance between the pleochroism absorption, extinc¬ 
tion angle, and double refraction between this variety of hornblende found in the 
basic gneisses and the well-known “ basaltin ” or basaltic hornblende found in basic 
lavas. This rock also contains a considerable amount of titanoferrite, passing by 
alteration into leucoxene (secondary sphene). 
