144 HOLLAND: GEOLOGY OF THE NEIGHBOURHOOD OF SALEM. 



SUMMARY OF RESULTS. 



In 1889 Prof. A. Lacroix published a description of an inter- 

 esting series of pyroxenic and scapolitic gneisses said to have been 

 obtained by Leschenault de la Tour from the neighbourhood of Salem 

 and Ceylon. But as the result of a special investigation of the area 

 made in August 1897, f° r tne purpose of determining the localities 

 and geological relations of the rocks referred to by Lacroix, it was 

 found that many of the types were not obtainable at all from the 

 immediate neighbourhood of Salem, and some of them closely re- 

 sembled occurrences known in other parts of the civil district, as well 

 as in the adjoining district of Coimbatore. Leschenault de la Tour, 

 however, visited many South Indian districts besides Salem, and to 

 facilitate the further identification of localities an annotated trans- 

 lation of his geological observations is given as an appendix to this 

 paper (pp. 1 — 3 and Appendix). 



The districts of Salem and Coimbatore, from which Les- 

 chenault apparently obtained most of his specimens, together cover 

 an area of 15,000 square miles, and include a remarkable complex of 

 ancient gneisses, as well as younger, plutonic, hypabyssal members 

 of nearly every petrographical family. The specimens described by 

 Lacroix were consequently obtained from localities far too widely 

 separated to permit the assumption that they were obtained from 

 formations which are in the geological sense associated with one 

 another. Whilst, therefore, Lacroix's interesting description of the 

 South Indian pyroxenic and scapolitic rocks is valued by the Geolo- 

 gical Survey as an important contribution to our mineralogy, his 

 geological conclusions concerning the origin of the rocks, based on 

 petrographical similarities to the French divisions of gneisses, have 

 yet to be confirmed by field observations. 



The correlation of our " pyroxene-granulites" (charnockite 

 series) with the younger division of the French gneisses is, however, 



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