418 A. K. Coomdraswdmy — The Balangoda Group. 



the patience of the readers of the Geological Magazine I should 

 like some day to make an attempt to show how the trick is done, 

 and how ripple-mark concerns geologists, not as a mere unimportant 

 detail of rock-structure, but as an important factor and index in the 

 great problem of marine erosion. In the meantime I may refer to 

 Dr. Nansen's admirable epitome of the evidence of marine erosion in 

 his work above referred to, and also to Dr. Cornish's papers in the 

 Geographical Journal. 



VIT. — Contributions to the Geology of Ceylon : 

 III. The Balangoda Group. 



By A. K. CooMARAswAMY, B.Sc, F.L.S., F.G.S., Director of the Mineralogical 



Survey of Ceylon, 



rpHE name ' Balangoda group ' is proposed for a series of granitic 

 JL and pegmatite-like rocks, intrusive in, but distinct from, the 

 Charnockite series ; first met with in the Balangoda district, but 

 evidently widely distributed over a large area between Balangoda 

 and Hatton. The rocks are best described as granites, but occur 

 most often in rather narrow dykes, after the manner of pegmatites. 

 Yet there is no reason for separating the smaller from the larger 

 masses, and the term granite is applied to both. The group (of 

 which a more detailed account will ultimately be needed) includes 

 in particular zircon granite, allanite granite, magnetite granite, and 

 granite without conspicuous accessory minerals ; as well as the 

 probably similar rocks in which the hitherto unlocated minerals 

 geikielite, baddeleyite, rutile, fergusonite, thorite,' thorianite, etc., 

 may be looked for ; and the vein of pegmatite at Gampola, which 

 consisted of quartz, felspars, and biotite, with apatite, ilmenite, 

 tourmaline, and the new mineral described as thorianite ^ as accessory 

 minerals. 



These granites are intrusive in the Charnockite series, and though 

 frequently occurring in lenticular masses (Denagama) with a dis- 

 position parallel to that of the foliation planes of the charnockites, 

 have often been observed to transgress these foliation planes and to 

 behave as intrusive rocks. Contact phenomena have not, however, 

 been observed, except perhaps in a slight tendency to a peripheral 

 fineness of grain in the intrusive rocks. At the junctions granite 

 and charnockite are usually welded together, there being no 

 absolutely hard line of separation, although the junction may be 

 called sharp ; in the case of the larger masses no good junctions 

 have been seen. 



A description of the rocks is given below, with special reference 

 to the localities where they can be seen : — 



Zircon granite. — This rock was seen in sitii at several points, and 

 is the best known member of the group. The finest and longest 

 exposure is on Massena estate, six miles from Balangoda ; here 

 a considerable mass of granite, fully two miles in length and 



' W. Dunstan, Nature, 1904, p. 510. 



* " Spolia Zeylanica," vol. i, pt. 4 (190-1), p. 112 ; and Nature, loc. cit. 



