364 A. K. Coomdraswdmy — Intrusive Pyroxenites 



the Charnockite Series or granulites) of Massena estate, Balangoda, 

 appears to indicate tbat the date of the pyroxenite intrusions was 

 long posterior to that of the intrusion and consolidation of the 

 granulites. Nevertheless, careful examination of the junctions shows 

 that there is never any sign of a chilled edge, but the pyroxenic 

 rock passes, rapidly indeed, but never abruptly, into the granulitic 

 rock next to it, and this even where the intrusive character is other- 

 wise most distinct. There is, in fact, a I'apid transition from one 

 rock to the other. Inasmuch as tlie pyroxenites are intrusive in 

 rocks which had cooled sufficiently to allow of the formation of 

 joints, these facts seem to show that re-melting must have taken 

 place to some extent. 



A zoned structure is very characteristic of the rocks, the zoning 

 being marked by the distribution of mica in bands parallel to the 

 edges of the dyke or sill, the individual crystals of mica being 

 disposed in planes perpendicular to the edges of the dyke or sill, 

 which is often symmetrical in structure about a median line, after 

 the manner of mineral veins. The zoned structure is not always 

 produced by mica ; in Fig. Ill, PI. XX, p. 366, for example, the 

 central darker zone is distinguished by its content of hornblende, 

 and mica is not present. 



The pyroxenites seem to be in some way connected both in 

 mineral composition and in actual distribution with the occurrence 

 of crystalline limestones, though the exact relation is not perfectly 

 clear. One curious feature is the presence of carbonates in parts of 

 the dykes, especially at Ella (Uva) and Kadawat Oya (Sab.) ; when 

 it becomes abundant, the central zone is sometimes indistinguishable 

 from an ordinary crystalline limestone with abundant accessory 

 minerals. 



A more detailed account of various exposures (especially those 

 illustrated) will now be given ; the localities described have been 

 visited at various times during the last two years. 



1. At Ella (Uva) are interesting exposures (Fig. I, PI. XX, p. 366) 

 in the bed of the Kitul Ela, just below the point at which it is 

 joined by the small stream from near the Rest House. The main 

 part of the intrusive rock consists almost entirely of granular 

 greyish-green diopside (1152) ; ^ in parts scapolite and a little 

 granular sphene are also present, and more locally hornblende 

 or mica. A section (1153) through the junction with granulite at 

 the point X in the figure shows granulite (a rock composed of 

 quartz and orthoclase with a little pale-green diopside) passing 

 very rapidly but with no loss of continuity into a granular rock 

 consisting of colourless diopside with scapolite and a few rounded 

 grains of sphene. At one point in the exposure a large crystal of 

 diopside projects from the pyroxenite into the granulite, merely an 

 exaggeration of the usual interlocking of minerals at the junction. 

 The inner portion of the pyroxenite (at li) becomes rich in 

 carbonates, and the relation to the rather impure granulites at g^ 



1 The numbers in brackets refer to thin sections in the author's collection. 



