334 MVashingto?i — CharnocTcite Seines of Igneous Rocks. 



specially striking peculiarities. Biotite is almost wholly 

 absent. The ores are either ilmenite or a titaniferous magne- 

 tite, and form a constant, though subordinate constituent. 

 Holland mentions garnet and titanite in some cases, but they 

 were not seen in my specimens. 



Chemically, the series shows a very great range in silicity, 

 SiO„ varying from 77*5 to 47*5 per cent. Alumina is rather 

 low, never more than enough to satisfy the combined alkalies 

 and lime, and its amount is fairly constant. The iron oxides are 

 high, with FeO greatly predominating over Fe 2 3 . Except in 

 the pyroxenite, magnesia is low, and consistently below the 

 iron oxides reckoned as FeO. Lime also is not high, but a 

 notable amount of it is always present, even in the most silicic 

 rocks. However, its amount is generally not more than enough 

 to satisfy the excess of alumina over alkalies to form the 

 anorthite molecule, except in the most femic members, where 

 a small part of it enters the diopside molecule as modal horn- 

 blende and augite. The alkalies are rather high and soda dom- 

 inates largely over potash, except in the charnockite where the 

 amounts are about equal. Titanium, phosphorus, and manga- 

 nese are consistently low, and the rocks carry but traces of 

 barium, strontium and chromium, and no zirconium. 



Comparison xoith other Regions. 



Comagmatic regions comparable with that of southern India 

 are few, though widely scattered. Those which can be surely 

 correlated, as has been suggested by the petrographers who 

 described them, are : the Ekersund, Soggendal and Bergen 

 Districts in western and southwestern ISTorway ;* the eastern 

 part of Ellesmere Land and Prudhoe Land opposite across 

 Smith Sound ;f the " Cortlandt Series," near Peekskill, Kew 

 York ; J and the Ivory Coast, in West Africa.§ Another sim- 

 ilar region in the Blue Ridge of Virginia has been studied by 

 T. L. Watson, whose description appears in the Bulletin of the 

 Geological Society of America, 1915. 



It has been suggested that the anorthosite area of Yolhynia |j 

 is also analogous to the Indian district. There is also much in 

 common with the anorthosite areas of eastern Canada*J[ and the 



*C. F. Kolderup, Berg. Mus. Aarb.. 1896, No. v; ditto, 1903, No. 12. 



\C. Bugge, Rep. 2nd Fram Exp., No. 22, 1910. 



JG. S. Rogers, Ann. N. Y. Ac. Sci., xxi, p. 11, 1911. This paper gives a 

 complete bibliography. 



§A. Lacroix, C. R., el, p. 18, 1910. 



|| K. v. Chrustchoff, T. M. P. M., ix, p. 470, 1888. Apparently the prom- 

 ised subsequent papers, including the chemical analyses and discussion, 

 were never published. 



U F. D. Adams, N. J. B. B., viii, p. 419, 1893 ; Can. Geol. Surv., Ann. Rep. 

 viii, J., p. 96, 1896. 



