Vol. 58.] WOLLASTONITE-SCAPOLITE GNEISSES OF CEYLON. 681 
The chief rock-types may be briefly tabulated as follows, though 
numerous transitions from one type to another occur :— 
ERNIE. ccloce senses 2s 1. Pyroxene-sphene-scapolite rock. Specific gravity =3'34. 
(2. Rocks composed of pyroxene, scapolite, wollastonite, and 
graphite, iron-ores, and sphene, often with subordinate 
felspars or quartz.! Specific gravity =2'99, 2°92. 
3. Similar rocks, with abundant orthoclase-microperthite, or 
| 
INTERMEDIATE. ¢ 
| 
\ quartz, or both. Specific gravity =2°90, 2°83, ete. 
( 
4, Rocks formed of orthoclase-microperthite, orthoclase, 
| oligoclase ; with very little pyroxene, sphene, graphite ; 
hee often rather coarser-grained than types 2 & 3. Specific 
se ceercesees 4 gravity =2'64, 2:60. 
| 5. Coarse-grained quartzofelspathic rocks of granitoid 
\ aspect. 
Types 1, 2, & 3 have usually a granular structure, types 4 & 5 a granu- 
litic structure. Types 2, 3, & 4 form the main part of the exposures. 
There are also (6) acid rocks composed of felspars, quartz, and little augite, 
iron-ores, apatite, zircon, etc., occurring as dykes crossing the foliation ; and 
(7) coarse wollastonite-orthoclase-quartz-pegmatites. 
The acid types (4 & 5) are of somewhat later origin than the 
basic, and though generally interbanded, behave on the whole in 
an intrusive manner towards them. The latest-formed dykes and 
segregation-veins (6 & 7) crossing the foliation are also of an acid 
type. 
Foliation.—The alternation of grey and white rocks of types 
4 & 5 with green and green-and-white rocks of types 2 & 3 produces 
aconspicuous banding. (Fig. 1, p. 682; see also Quart. Journ. Geol. 
Soc. vol..lvi, 1900, p. 602, fig. 2.) At thejunctions of the different 
bands there is a gradual but rapid change from one type to the other. 
Quartz, when present, is usually in individuals elongated parallel to 
the foliation ; flakes of graphite are similarly oriented, and when 
locally abundant may even produce a plane of parting. The 
general strike varies little. Occasionally sharp contortions are to 
be found, the axes of the sharp folds being parallel to the strike. 
These local sharp folds are the result of pressures acting during 
consolidation. 
Dykes and segregation-veins.—A few dykes of normal 
charnockite-like type are found, crossing the foliation at right angles 
or obliquely. Such dykes are from 1 to 4 feet wide, and con- 
sist of grey and greenish-grey rock, not especially coarse-grained, 
in which very fine-grained orthoclase-microperthite is a predominant 
mineral, with quartz, a little augite, and sometimes apatite, sphene, 
and iron-ores. as accessory minerals. They have a specific gravity 
varying from 2°62 to 2°67. One such dyke showed traces of a banded 
structure parallel to the edges. At the junctions with the matrix, 
1 In most cases, not quite all the minerals mentioned occur in the same 
slide, 
