TRANSACTIONS OF SECTION C. 563 



however, also possible that these superficial and somewhat polygonal hollows in 

 the luverell diamonds may not be of the nature of negative crystals formed 

 by corrosion, but rather external casts of some mineral once associated with the 

 diamond, but since removed by absorption. 



On the corrosion-hypothesis, the diamonds may have crystallised out from the 

 magma of the hornblende-diabase at no very great depth below the spot where they 

 are now found. At all events these cavities, to which attention was first calltd 

 at this meeting by Professor Bonney, show that the Inverell diamonds did not grow 

 exactly at the spot where they have now been found. The corrosion may have 

 been due to the diamond becoming more fusible as pressure was relieved in the 

 course of its passage upwards from the magma reservoir. 



The experimentsof Dr. Friedla,uder,of Bei iin, have proved that minute diamonds 

 can be made by stirring a molten magnesian silicate like olivine with a black- 

 lead pencil, and in the Novo-Urei Meteorite diamond has been found associated 

 with magnesian silicates. 



In view of these facts it is quite possible, in the writer's opuiion, that the 

 hornblende-diabase magma may have been the true parent rock of the Inverell 

 diamonds. 



3. On the ' Cidlinan ' Diamond. By F. H. Hatch, Ph.D. 



4. Exhibition of a Remarkable Form of Sodalitefrom Bajputana. 

 By T. H. Holland, F.K.S. 



Nearly every discovery of the interesting family of nepheliue syenites shows 

 some feature of unusual interest amongst igneous rocks. The latest-discovered 

 occurrence of these rocks in India is remarkable for the presence of a form of 

 sodalite which has the property, apparently unique amongst minerals, of rapidly 

 changing colour in bright daylight from carmine to pale grey or colourless, and 

 of slowly recovering its carmine colour when kept in the dark. The mineral 

 with these peculiar properties was discovered by Mr. E. Vredenburg as a con- 

 stituent of the pegmatitic veins in a nepheline syenite intruded into the 

 Aravalli schist series of Kishengarh in Kajputana. Along the same belt the 

 sodalite, intergrown with nepheline in the pegmatite veins, is of the common 

 blue variety, and nothing unusual is shown by chemical analysis of either variety. 

 The carmine colour disappears as rapidly on exposure to light in a moist 

 atmosphere as in dry air, in the cold weather as rapidly as at higher tempera- 

 tures, and under bright electric light as in daylight. The mineral has apparently 

 no ettect on a photographic plate, and is not noticeably radio-active. The 

 reappearance of the carmine tint takes place in a few weeks in some specimens, 

 but requires some mouths' concealment in the dark in others. No explanation 

 has been oli'ered so far to account for this remarkable phenomenon, and the 

 specimens are now exhibited with the hope of obtaining suggestions for a 

 systematic investigation of the mineral. 



5. Fourth Refort on the Fauna and Flora of the Trias of the 

 British Isles. — See Reports, p. 293. 



6. A Contribution to our Enowledye of the Limestone Knolls of Craven. 



By A. WiLMOKE. 



The Craven Lowlands district, between the great faults on the north-east and 

 the grit hills of the Pendle Range on the south is characterised by a well-known 

 series of limestone knolls which have been the subject of much discussion.' 



' Tiddeman, Urit. Assoc. litp., 1H99; Brit. Assoc Handbook fur Leeds and 

 Aircddlc, 1S90 ; Brit. Assoc. Rei)., lUOO; Gcol, Marj., January 1001. Marr, Q ./.G.S.. 



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