l6S HOLLAND: CHARNOCKITE SERIES. 



Williams found these two minerals, together with sillimanite, in the 

 Cortlandt series of New York, 1 and compared the occurrence with 

 the previously better-known similar association of these minerals 

 with the pyroxene-granuiites near Ronsberg on the eastern edge of 

 the Bohemian forest, whilst very numerous similar instances have 

 recently been found in South India 2 The occurrence of the green 

 spinel as a simple constituent of the series as well as a contact product 

 of the pyroxenic rocks adds another instance to the already numerous 

 examples which show that the distinction between simple igneous 

 rocks and highly metamorphosed products cannot be marked by a 

 sharp line. 



The green spinel in these pyroxenites occurs in irregularly 

 shaped granules and sometimes vermiform blebs, associated invari- 

 ably with lumps of magnetite and generally crowded with minute 

 granules and dust of presumably the same substance. Where the 

 crystallization has been very coarsely developed we frequently find 

 cubic crystals of magnetite lying in the green spinel, which, except in 

 the immediate neighbourhood of the magnetite crystals, is crowded 

 with magnetite dust. From the immediate precincts of each magne- 

 tite crystal the dust has been completely removed and a clear green 

 zone indicates the extent of its n crystal court." 



In one case of a hypersthene pyroxenite from the Salem 

 District (sections 1030 and 1031) the green spinel is generally seen to 

 be surrounded by a zone of a pale-pink, isotropic and highly refracting 

 mineral, which is presumably the ordinary magnesia-alumina spinel. 8 

 In this case, therefore, the spinelloids are represented by three 

 different types formed apparently in an order which indicates a 

 gradual decrease in the protoxide and sesquioxide of iron and a 



1 Amer. Journ. Sci., Vol. XXXIII (1887), p. 194. 



2 See Manual of Economic Geology of India, 2nd Edition, 1898, pp. 12, 13, 14, 18,* 41 

 and 45. 



« The specimen from which these sections were cut I found in the Madras Museum 

 labelled " Salem district," but without any further details as to its origin. Judging- from the 

 slides the rock must be a most remarkably interesting one, and it is extremely unfortunate that 

 in consequence of the absence of details as to its precise locality we are unable to examine its 

 geological relationships. 



( 50 ) 



