168 - i MR. C. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
pebbles of the latter are met with in the old gravel beds of the Mobaychoung, in the 
vicinity of Nyoungouk. 
5. Gneissic Rocks. 
As before stated, the rocks composing the earth’s surface over the large extent of 
country embracing the ruby mines tract are composed chiefly of gneiss. These are 
covered in places by hill-wash on the mountain sides, and alluvial deposits in the 
valleys, but every here and there they appear at the surface in large exposures, 
enabling their varieties and structure to be studied. They contain bands of 
crystalline limestone of various thicknesses, which form a subordinate, though most 
important, part of the whole, insomuch that all along their outcrops are situated the 
gem mines which form the chief industry of the district. 
The chief variety of gneissic rocks met with is a hard, coarse-grained, grey 
compact gneiss of somewhat massive character, which shows its true foliated structure 
by the weathering of its surface. This passes into a fine-grained gneiss of lighter 
colour and finer foliation, which in parts shows a slight contortion of its foliation. In 
a few places some of these show a very contorted foliation, and resemble the form 
once known in Germany as Stangel gneiss. Amidst the ordinary gneisses there 
occur massive and thin interfoliated layers of a rock composed almost entirely of 
quartz and felspar, the latter often in very large crystals, which sometimes assumes 
the character of an ordinary graphic granite. For this rock I employ the term 
pegmatite. It does not, as far as I was able to observe, constitute veins or intrusive 
masses, but forms a member of the gneissic series with which it is interfoliated, and 
possibly interbedded. This bedded character, both in this rock and in the gneiss, 
may be in appearance only, and due to tabular jointing, coinciding with the planes of 
foliation ; but when examining such exposures as those of Chenitaung mountain 
and on Toungnee pass (to be afterwards described), one cannot but be struck with 
the resemblance of this to true bedding. The last variety to be mentioned, though 
not extensively developed, is seen on the range north of Kathay, near Sagiwa 
mountain, and also near Bernardmyo. It is of a coarse texture, of a greenish to 
greenish-yellow colour, and of a somewhat waxy appearance, containing in places 
sparsely scattered crystals of black mica, similar to that sometimes seen in the coarser 
pegmatites. A layer of dark liornblendic rock is met with in a few places, which 
may be a hornblende gneiss, but it occupies only a very subordinate position. 
The main range on the south side of Mogok valley, from Chenitaung to Panma, is 
composed of gneiss of the massive, coarse variety; but to the southward it passes 
into the lighter and finer textured sorts, with interfoliated pegmatite, almost as far 
as the Mobaychoung. 
The mountains north of Mogok, and onwards to Bernardmyo, are principally formed 
of the hard, finely-foliated variety; and a similar gneiss is also well developed south 
of Kyatpyen and Kathay. 
