376 A. K. Coomdraswdmy — Crystalline Limestones of Ceylon. 



almost always exceedingly fresh. The calcite and lime-silicates 

 found near the junctions are not the result of alteration of minerals 

 composing the granulites. Contact-metamorphic relations between 

 the limestones and granulites are everywhere indicated. 



Dr. Callaway has suggested that the crystalline limestones of 

 Bodwrog and Forth Trecastell in Anglesey,^ and of Ceylon,^ may 

 have originated by " segregation from plutonic rocks during 

 deformation." That the Ceylon limestones have not been formed 

 thus is shown by the contact-metamorphic relations between them 

 and the granulites, and the freedom from deformation of the latter, 

 with which they are inseparably associated, 



Mr. Holland ^ has suggested that the crystalline limestones of 

 Burmah may have existed in a state akin to fusion. Calcite has 

 been claimed as an original mineral in nepheline-syenite by more 

 than one observer.* The present writer has described what is 

 probably an original intergrowth of calcite with quartz.^ 



I have recently given some account of the crystalline limestones 

 of Ceylon,^ showing that a vast series of granulites, various in 

 chemical and mineralogical composition, is there most intimately 

 associated with a smaller but widely distributed series of crystalline 

 limestones occurring in bands of various widths, whose foliation 

 (dependent on variations in coarseness of grain, structure, and 

 mineral composition) is parallel to that of the granulites and to the 

 boundaries between the two rocks. The contact phenomena and the 

 transitions between the two types of rock are also described. 



As to the real origin of these limestones, not very much can be 

 said. We might regard them as altered sedimentary or even 

 tufaceous rocks, which the intrusive granulite has melted and 

 partially absorbed. The wollastonite-scapolite gneisses of Galle 

 might, on this supposition, result from the total absorption of 

 a large mass of limestone by the granulites. It may be objected, 

 however, that there is little or no evidence of the existence of other 

 altered sedimentary rocks such as would probably have accompanied 

 the limestone,'' and that the limestones occur in different areas, 

 sometimes abundantly and in wide bands, sometimes in narrow 

 bands far removed from other rocks of the same sort. 



1 Eep. Brit. Assoc, 1887, p. 706. 



~ Geol. Mag., 1902, p. 285. 



3 Mem. Geol. Surv. India, 1901, vol. xxx, pt. 3, p. 175. 



* Holland : Mem. Geol. Surv. India, loc. cit., p. 197. Adams : Amer. Journ. Sci., 

 1894, vol. xlvui, p. 14. 



^ Quart. Jom-n. Geol. Soc, 1900, vol. Ivi, p. 606, also pi. xxxiii, fig. 1. 



•^ Quart. Journ. Geol. Soc, 1902, vol. Iviii, p. 399. 



'' I have met with roots almost composed of dark mica in one or two localities 

 (Yatirawana, near Wattegama, and Talbot Town, Galle) associated with the 

 granulites. Almost any mineral occui'ring in the granulites may, however, be 

 sometimes met with in this way as a main constituent of a local variety. It is, 

 however, quite true that some varieties rich in garnet and biotite are not altogether 

 unlike much altered sedimentary rocks, though I do not myself regard them as such. 

 Lacroix has described some rocks in which andalusite, sUlimanite, and corundum 

 occur, but unfortunately the localities in Ceylon are unknown. Possibly these 

 minerals indicate the existence of altered sedimentary rocks, but this is by no means 

 necessarily the case. 



