368 A. K. Coomdrcmcdmy — Intrusive Pyroxenites, Ceylon. 



long). The magnesian silicates and scapolite are idiomorphic 

 towards the calcite and present a handsome appearance in weathered 

 specimens. 



In the Uma Oya below there are numerous exposures, both of 

 ' thread dykes ' and of intrusive pyroxenic and micaceous rocks, as 

 well as of coarse felspathic pegmatites, with which their relations 

 are somewhat confused. 



7. Of pure mica rocks or veins there may be instanced those 

 described in the (first) " Administration Eeport of the Mineralogical 

 Survey," Colombo, 1904. Analyses of mica will be found in 

 Professor W. E. Dunstan's "Reports on the Results of the Mineral 

 Survey [of Ceylon] in 1903-4," London, 1905. 



One example of a mica rock or vein may be quoted from the 

 (second) " Administration Eeport of the Mineralogical Survey," 

 Colombo, 1905, p. 20. A large vein of brown phlogopite is exposed 

 in the Mineran Oya, just within the boundary of Sherwood estate 

 (about nine miles north of Balangoda), in the south-west corner. 

 The vein is about 5 feet wide, and strikes 20° N. of E. and hades 

 70° S.S.E., and crosses the foliation of the granulites, which are 

 inclined at low angles. The Oya has for some distance cut its way 

 along the mica vein, which is exposed in the bed of the stream. 

 The largest crystals are 18 inches in diameter, but somewhat flawed. 



8. A fairly typical zoned mica pyroxene dyke, from 2 inches to 

 1 foot wide, is found cutting the zircon granite (Balangoda group) 

 of Massena estate, Balangoda. As the zircon granites are them- 

 selves intrusive in the granulites,' the pyroxenic intrusions would 

 thus appear to be removed from the date of intrusion of the 

 material composing the Charnockite Series, by the period required 

 for the intrusion of the Balangoda group. 



Canadian analogies. The rocks described closely resemble the 

 pyroxenic rocks associated with the apatite deposits of Canada, 

 described by A. Osann ("Notes on certain Archean Eocks of the 

 Ottawa Valley," Geol. Surv. Canada, part 0, Ann. Eep., vol. xii, 

 1902), and by C H. Gordon ("Pyroxenites of the Grenville Series 

 in Ottawa County, Canada," Journal of Geology, vol. xii, No. 4, 

 1903, pp. 316-325), who states that the evidence there too "clearly 

 warrants the conclusion that the pyroxenic rock is intrusive." 

 Detailed descriptions and further references will be found in the 

 papers mentioned. 



Summary. A group of pyroxenites, in which the minerals 

 diopside, phlogopite, hornblende, and scapolite predominate, while 

 sphene, plagioclase, pyrite, apatite, and spinel are often accessory, 

 occurs in small sills and dykes intrusive in the Charnockite Series 

 or granulites, and in one case apparently also in a zircon granite 

 of the Balangoda group. The pyroxenic intrusions have usually 

 a zoned or laterally symmetrical structure analogous to that of 

 mineral veins. The intrusive material never shows a chilled edge, 



1 A. K. Coomaraswamy, "The Balangoda Group": Geol. Mag., 1904, 

 pp. 418-422. 



