54 MONCHIQTJITE FEOM MOTJKT GIENAE, JFNAGAEH. [Feb. IQOI, 



the analcime was formed by aqueous agents after the consolidation 

 of the monchiquite. This probability was strengthened by the fact 

 that analcime had been formed artificially in the laboratory from 

 both nepheline and leucite. Stewing in a solution of soda appeared 

 to be all that was necessary to convert leucite into analcime. He 

 had sometimes been asked why leucite was found in such restricted 

 areas : he thought that one cause for this was that leucite was 

 readily converted into analcime and other secondary minerals ; and 

 consequently, in rocks of considerable geological age, the leucite that 

 they may originally have contained had long since been converted 

 into secondary minerals. The rounded discs filled with analcime, 

 shown in the slides exhibited on the screen, were yery suggestive 

 of pseudomorphs after leucite. The presumption in favour of the 

 analcime in the rock described by the Author being a secondary 

 mineral seemed so great that an igneous origin ought not, in 

 the speaker's opinion, to be assigned to it, unless the verdict was 

 supported by very cogent evidence. 



Prof. Jfdd pointed out that in his paper the Author had not only 

 given a very clear statement of the whole problem of the presence 

 of analcime as an original constituent in igneous rocks, but had 

 added two fresh facts in support of the contention that such 

 associations actually exist. His recognition of the cleavage and 

 crystalline form of the substance appeared to be new, and con- 

 stituted certainly very valuable results. 



Mr. Haekee said that this paper afi'orded additional evidence that 

 the interstitial isotropic substance of the monchiquites is not glass 

 but analcime, and is an original igneous product. The primary or 

 secondary origin of the analcime-spheroids is perhaps a more 

 doubtful question, and there seems to be room for suspicion that 

 these may be pseudomorphs after leucite — a suspicion strengthened 

 by their richness in potash. Whatever the interpretation, this 

 Indian occurrence presents numerous points of interest. 



The PEEsiDEiirT and Prof. Watts also spoke. 



The AuTHOE stated, in reply to Mr. Prior, that it was uncertain 

 whether these rocks were an inlier in the Deccan Trap or repre- 

 sented a deep-seated portion of the same igneous series. In the 

 latter case they would be of late Secondary or early Tertiary age. 

 in answer to Gen. McMahon, he referred to the fact that some, 

 perhaps most, igneous magmas contained a considerable amount of 

 water, as was shown by its occurrence in glasses which, like many 

 pitchstones, had consolidated under pressure. There was no reason, 

 therefore, why minerals containing the elements of water should not 

 crystallize from fusion if the pressure were sufficient to prevent the 

 separation of the water from the magma in the form of steam : 

 biotite was an example of such a mineral. With regard to 

 Mr. Harker's doubts as to the formation of anhydrous substances 

 such as nepheline and orthoclase from a hydrous mineral like 

 analcime, the Author suggested that it was analogous to their 

 crystallization from an igneous magma containing water. In the 

 latter case the nepheline and felspar were formed directly from the 

 magma, in the former analcime represented an intermediate stage. 



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