Vol. 56.] 



CEYLON ROCKS AND GRAPHITE. 



603 



this kind are far from evident : it is important to notice that they 

 closely resemble rocks from Nilhene, which appear to be vein- 

 products. 



A series of rock-exposures is found in the grassy area next the 

 sea-wall of the fort, especially near the flagstaff. The rocks are of 

 exceptional mineral composition, and mineral-banding is very con- 

 spicuous (see fig. 2, p. 602) ; the appearances resemble those which 

 would result from movement in a non-homogeneous magma. A large 



specimen from the 



Pig. S.—Ophitic plate of wollastonite (W), middle of the ex- 



enclosing idiomorphic quartz (Q,), pyroxene, posure seen in the 



(P), and felspar (F). figure, varies from 



a moderately coarse 

 pegmatite to a 

 finer-grained rock 

 in which the sepa- 

 rate minerals are 

 scarcely recogni- 

 zable macroscopi- 

 cally. The pegma- 

 titic portion shows 

 idiomorphic quartz, 

 green pyroxene, 

 and rarer ortho- 

 clase embedded in 

 a large individual 

 of wollastonite 

 (fig. 3). The clea- 

 vage-faces of the 

 wollastonite have 

 a pearly lustre and a striated surface. It breaks up readily in a 

 fibrous way, and in some of the flakes the emergence of two optic 

 axes may be seen in convergent polarized light, the open axial 

 plane being perpendicular to the elongation of the flakes. The 

 optical character is negative. From the large ophitic individual 

 material for analysis was obtained and supplied to Mr. Shepherd r 

 F.I.C. The results of his duplicate analysis are as follows : — 



I. II. 



Per cent. Per cent. 



Si0 9 51-28 54-59 



CaO 4555 40-85 



A1 2 3 2-01 1-77 



FeO 1-34 70 



Los3 on ignition not est. 2'29 



_100-_18 100-20 



Specific gravity = 2'76 2-78 

 These analyses correspond nearly to the formula 0aSiO 3 . 



