BY HENRY C. RICHARDS, M.SC 1) 



the earth'vS crust, so that we meet in successive peiiotls the 

 same tj'pes of rocks. 



It is not generally conceded that Loewinson-Lessiug 

 was justified in coming to the above conclusions on the 

 available evidence. 



" The Methods of Petro -Microscopic Research," by 

 F. E. Wright, which was published by the Carnegie Institu- 

 tion in 1911, was a most important contribution. Wright 

 justly states in petrology : "" The quality of our quantitative 

 work is far more important than the ([uantity of our quaUta- 

 tive work,"' and his publication is one which certainly 

 makes for increased efficiency in quantitative work. 



An interesting paper by L. L. Fermor, in 1912, on the 

 ■ .Systematic Position of the Kodurite Series "" in India, 

 ■discloses a novel idea in the use of garnet as a geological 

 barometer. 



Kodurite when classified according to the American 

 •classification, gives a iiorm of Orthoclase, Leucite, Apatite, 

 Anorthite, Hedenbergite, WoUastonite, Tephroite, and 

 Magnetite. The Mode is Orthoclase, a manganese garnet 

 knoAvn as Spandite, and Apatite. Comparison of the specific 

 gravities of the norm and mode of this rock showed that 

 the garnetiferous form (the mode) Avas of a consideralily 

 higher specific gravity and consequently occupied a con- 

 siderably smaller volume (10 per cent, less) than the non- 

 garnetiferous form (the norm). Fermor, therefore, con- 

 •cluded that Kodurite must have been formed under con- 

 siderable pressure and that below a certain depth all the 

 ferro-magnesian minerals, such as pyroxene, amphibole. 

 olivine, and biotite with anorthite have arranged them- 

 selves as far as possible into garnets, for thereb}' the maximum 

 reduction in volume and absorption of heat is effected. 



Fermor then goes on to suggest that beneath the rocks 

 now known as plutonic, there must be a zone of garnetiferous 

 rocks extending downwards in a plastic solid form as far 

 .as the presumed metallic core of the earth. For this zone 

 he proposes the term " Infra-Plutonic." 



Fermor's publication is very interesting and his con- 

 clusions ingenious, but in view of the occurrence of garnet 

 in certain limestone contact -rocks, etc., it Avould be better 

 perhaps to regard certain other minerals of high specific 



