( J^^ ) 



decomposition of the grauulites, especially from their felspathic 

 elements. 



Volcanic rocks are very sparingly represented in Ceylon. A 

 typical ilolerite (probably occurring as a dyke) from Kallodai, 

 Eastern Province, is represented in the collection, A few other 

 dykes are said to have been met with in Ceylon. No lavas or 

 tuffs occur, and, with the exception of a few hot springs, no signs 

 of volcanic activity are found. Denudation has been so long at 

 work that only the most deep-seated rocks are now exposed at 

 the surface. Of sedimentary rocks, we have (a) river g'nivels, 

 sands, and alluvial clays (used for brick making) deposited 

 by rivers. In the gravels are found the gems which have been 

 derived from the crystalline rocks ; many have not yet been found 

 in situ, (h) Marine deposits, including coralline raised beaches, 

 blown sand, &c. Fossil shells and corals are abundant in the 

 raised beaches which are found all round the coast and often some 

 little way inland, but never very far above the present level of 

 the sea. 



II.— MINERALS. 

 Before proceeding to refer in systematic order to the nature and 

 mode of occurrence of particular minerals it will be useful to 

 consider briefly their nature and mode of formation. Regarded 

 from this point of view the minerals of Ceylon fall into three 

 main groups, which are not, however, separated from each other 

 by any rigid line of demarcation : — 



A. — Minerals composing or associated with the crystalline 

 rocks. 



B. — Vein minerals. 



C. — Minerals which are alteration products of other minerals 

 and rocks. 

 The lirst class includes those whose origin is for the most part 

 directly igneous (i.e., the majority of Ceylonese minerals), and 

 which occur as original minerals in the granulites and crystalline 

 limestones. Many of these have crystallized from an actually 

 molten or viscous magma, others perhaps from masses of rocks 

 existing merely in a state akin to fusion, some being developed 

 as the result of contact interaction between the limestones and 

 granulites when both possessed a high temperature, whilst others 

 forming pegmatite veins may even have crystallized from heated 

 vapours or liquids saturated with mineral matter. When suitable 

 conditions prevail, these minerals each assume definite and charac- 

 teristic crystalline forms ; this has, however, rarely been the case 

 in the granulites themselves, where an irregular "granulitic" 

 structure usually prevails : in the crystalline limestones, however. 



