GEOLOGICAL RELATIONS AND ORIGIN. 171 



II.-GEOLOGICAL RELATIONS AND ORIGIN. 



Sivamalai (Shivenmulla of the Atlas Sheet, N0.61 ; lat. 1 1° 3'N., 

 long. 77 36' E.) stands up abruptly on the dry 



Disposition of exposures. . 



monotonous plain, three miles north-west of 

 Kangayam in the Dharapuram taluk, Coimbatore district. Looking 

 across the Tirrupur-Kangayam road from the summit of Sivamalai a 

 row of six or seven, small, rocky hillocks may be seen stretching in a 

 west-north-west or west by north direction as far as the village of 

 Karutapalaiyam. These small hillocks are found to be composed of 

 precisely the same rock as that which makes up the main mass of 

 Sivamalai, forming in fact a series of lenticular masses of elaeolite- 

 syenite lying in the crystalline schists, which in this area have a 

 general west-north-west — east-south-east strike of foliation. 



As is usual with such lenticular masses in the crystalline schists, 



the elaeolite-syenite forming Sivamalai and the 



Foliation. . J & 



string of small hills shows a marked linear 

 arrangement of its constituents parallel to the general foliation of the 

 rocks around. This foliation of the elaeolite-syenite, though not ac- 

 companied by definite banding, is so well marked as to be quite 

 noticeable in hand-specimens, and as the most prevalent variety is 

 comparatively fine in texture, and distinctly even-grained for an 

 elaeolite-syenite, the rock might very well be mistaken, on casual ex- 

 amination, for a common biotite-gneiss, as it was indeed originally 

 described. 



We are here confronted at once with a phenomenon which 

 constantly puzzles workers in a crystalline country, namely, the 

 occurrence amongst the ordinary crystalline schists of foliated lenti- 

 cular masses which in petrographical composition are essentially 

 similar to known eruptives. The pyroxene-granulites, pyroxenites, 

 amphibolites and peridotites are amongst the most prominent rocks 

 whose occurrences in this form have given rise to much controversy 



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