A. K. Coomdrasicdmy — The Balangoda Group. 421 



by a partial analysis made for Mr. Holland, and by Mr. G. T. Prior, 

 to whom a sample was submitted. The granitic dyke is composed 

 of quartz, felspar, hornblende, allaoite, biotite, pyrite. 



The felspars include porpbyritic orthoclase and also a series 

 of smaller individuals of orthoclase and plagioclase (some of the 

 latter are porpbyritic like the orthoclase), forming with quartz the 

 finer-grained portions of the dyke. Allanite and hornblende occur 

 in varying amount, both being locally very abundant. Biotite is 

 scarce. Pyrite occurs chiefly in secondarily deposited films. 



A better exposure of allanite granite is found in the lower part 

 of Denagama estate, about seven or eight miles from Balangoda. 

 A conspicuous dyke, three to four feet thick, crosses the left branch 

 of the stream, which runs through the tea below the path, and 

 forms a conspicuous ledge inclined at a low angle to the foliation. 

 The granulites are inclined at a very similar angle, but it can be 

 seen clearly that the dyke does not keep strictly to the foliation 

 planes ; moreover, a few short processes, six inches to a foot in 

 width, project into the rock underlying the dyke, clearly showing 

 the intrusive character of the latter. The dyke is coarse-grained, and 

 consists mainly of orthoclase (porpbyritic idiomorphic individuals 

 often about 3x1 inches), quartz, and biotite, the latter in long thin 

 crystals (measuring e.g. 9 X 1 X ^ inches) scattered in all directions 

 through the rock. 



In these two dykes the allanite is very unevenly distributed, 

 being in places very abundant, and elsewhere almost or quite absent. 

 The allanite forms thin tabular idiomorphic as well as more irregular 

 individuals; the largest attain a length of three inches, those of 

 medium size measure about 1 X ^ X ^ inch. A curious point is 

 that the allanite seems to form a centre for radiating cracks in the 

 rock, giving it a rather conspicuous appearance, of which a diagram 

 is given in Fig. 2 (Denagama). 



The allanite is macroscopically black (in thin section brownish 

 olive-green), and has a resinous lustre and conchoidal fracture ; 

 hardness about 6 ; sp. gr. 3*2 to 3-5 ; before the blowpipe it 

 intumesces strongly. 



Magnetite granite. — A small dyke 2 inches wide and of the usual 

 character, but containing irregular individuals of magnetite about 

 1^ inch in diameter, was seen in the bed of the Wewel Dola at Dik 

 Mukulana. Another dyke 6 inches wide, containing similar 

 magnetite, was observed on Hopewell estate. 



The Gampola pegmatite.^ — This rock consisted mainly of orthoclase, 

 quartz, and biotite, and contained apatite, tourmaline, ilmenite, and 

 uraninite (' thorianite ') as accessory minerals. 



Granites without conspicuous accessory minerals. — These are of 

 fairly general distribution in the Balangoda district, sometimes 

 occurring in the form of dykes (usually less than three feet in 

 width) in very considerable abundance. It is possible that a much 

 more extended search might reveal the presence of macroscopic 

 zircons in some of these rocks ; for the most part, however, they 



1 " Spolia Zeylanica," vol. i, pt. 4 (1904), p. 512. 



