part 4] ox the miocene of ceylon. 579 



in which gasteropoda are common, and appears to represent 

 accumulations associated with ancient coral-growth. The rock 

 usually weathers into a honeycombed mass. 



The following petrographic notes were made in the Geological 

 Department of the University of Birmingham. 1 have to thank 

 Prof. W. S. Boulton for placing a microscope and other facilities 

 at my disposal. 



Sections of limestones from Kirimalai and Pallai (Jaffna pen- 

 insula) and north of the Pomparippu (North-Western Province) 

 agree very closely. They are sand-free foraminiferal limestones 

 with remains of calcareous algae (Litliotltamnium), echinoid- 

 radioles, and molluscan tests, set in a cement of crystalline calcite. 

 Another from Puttalam (North-Western Province) shows fewer 

 complete tests of foraminifera, and the matrix is a consolidated 

 limestone-mud. Another from the bed of the Kal Aru is distin- 

 guished by containing small derived pebhles of material similar 

 to the rock itself; much iron-staining is present, and in several 

 instances ferruginous material tills the interior of foraminifera] 

 and other tests. 



In addition to these pure limestones, grits with calcareous 

 cement occur at several localities, at one of which they contain a 

 fauna similar to that of the limestones. At Kirimalai the grit 

 (here fossiliferous) has grains mostly of quartz, extremely angular 

 and small (OT to 02 mm..), with a few comparatively large grains, 

 some exceeding 2 mm. in diameter. Grains of a black iron-ore, 

 possibly ilmenite, hut more probably magnetite, are present; garnet 

 occurs sometimes, while zircon, tourmaline, corundum, monazite, 

 and biotite are still less common. One slide contains a few small 

 pebble-like inclusions of angular quartz-grains set in an iron- 

 stained calcareous matrix. Iron-staining occurs elsewhere in small 

 patches in the slides. Between Karuvalakuda and Palugahatuve 

 a similar grit occurs ; but the quartz-grains are larger (025 to 

 0"G mm.) and less angular, garnet and black iron-ore are more 

 abundant, and there are tiny pieces of fibrous minerals, apparently 

 sillimanite and wollastonite. Apart from molluscan tests Idled 

 with large calcite-crystals, there are few organic fragments. Near 

 Point Pedro the limestone contains a good deal of quartz-sand ; 

 while ninth of Palavi there is a calcareous conglomerate containing 

 quartz-pehbles which measure an inch or more in length. 



Occasionally along the beach, particularly near Point Pedro, 

 grey and brown chert-pebbles closely resembling Hint are to he 

 gathered ; they probably represent the remains of silicilied layers 

 of limestone. Examples of this replacement are not known 

 in situ ; but some pieces of opaline material containing charac- 

 teristic limestone fossils, picked up on the mainland in the dry bed 

 of the Kal Aru, suggest very strongly that such local replacement 

 has occurred. ruder the microscope, this material from the 

 Kal Aru is seen to consist of opal and chalcedony showing 

 botryoidal structure in cavities : there are many unidentifiable 

 traces of organisms. 



