A. K. Gaomdraswdmij — Crystalline Limestones of Ceylon. 377 



Whatever their original character may have been, the limestones 

 must have existed before the intrusion of the granulites. I think it 

 is clear, however, that in their present condition the two rocks are 

 ' contemporaneous,' and this is shown by their intimate associations 

 and similar behaviour, and by the transitions from one rock to the 

 other which sometimes occur. I suggest that the limestones them- 

 selves have existed in a state akin to fusion ^ and have behaved much 

 as igneous i-ocks, and that the carbonates entering into the con- 

 stitution of the granulites near the contacts are, as they appear to 

 be, original minerals.- That the limestones have existed in a state 

 akin to fusion is shown, I think, by the appearances of flow-structure 

 (foliation),^ the occasional porphyritic structure, the aggregates of 

 accessory minerals (which correspond perhaps to the basic secretions 

 of some igneous rocks), the intergrowths of calcite and dolomite, 

 and by the field relations of the limestones and charnockite series. 

 The accessory minerals have crystallized out as if from a magma. 

 The limestones may have been softened before the intrusion of the 

 granulites (which greatly exceed them in amount), or have become 

 so as a result thereof. Each rock has been affected near the contact 

 by the absorption of material from the other, the granulites showing 

 the more conspicuous modifications. This transference of material 

 is shown in the granulites near the junctions by the appearance 

 of minerals rich in lime, such as scapolite, sphene, diopside, 

 phlogopite, and calcite, and in the limestones by the appearance of 

 minerals such as diopside, amphibole, phlogopite, and spinel, and 

 very rarely scapolite and felspar. The common occurrence of spinel 

 as a contact mineral seems to result from the appropriation of all 

 available silica in the formation of lime-silicate minerals, leaving the 

 oxides to form spinel. 



The whole process must have taken place under conditions of 

 great pressure. Differential movements during consolidation have 

 produced the conspicuous foliation. To some extent the limestones 

 and granulites have been rolled out together during consolidation, 

 and in this way sills of granulitic rock in the limestone have been 

 broken and portions separated, sometimes as lenticles continuing 

 along the strike the unbroken portions of the sill, sometimes to 

 form irregular patches or snaky twists of pyroxenic rock in the 

 limestone, sometimes to be found as quite isolated masses, surrounded 

 by the enclosing limestone. 



To summarize, I wish to suggest — 



(1) That contact-metamorphic relations between the limestones 

 and the charnockite series are everywhere clearly indicated. 



^ The direct use of the term ' molten ' is avoided, iaasmuch as we can know hut 

 little of the conditions of matter imder very great pressiu'e, and it is inadvisahle to use 

 the same terms in the description of conditions which, though analogous, must yet be 

 very different. 



2 Cf. J. J. H. Teall, Geol. Mag., 1886, p. 349. 



^ It is evident that the limestones have not (except very locally) suffered from 

 deforming earth-movements since the development of the accessory minerals, whose 

 varying abundance is largely the cause of the apparent foliation. 



