nol.% MgO+CaO 



Fig. I. The relation between the réfringence and the composition in the pyrope-almandite 



garnets, and the variation in the quantity of lime in the garnets from different rocks. 



Garnets from: • Olivine-rocks (i); © Eclogites (2); A Gabbros (3); ■ Amphibolites (4); 



Y Cordierite-rocks (5); + Gneisses and micaschists (61; x Granites I7). 



So much new material of garnet was gathered in the course of the 

 work that it seemed reasonable to make use of this fresh evidence con- 

 cerning the relations between the optical properties and chemical com- 

 position of the garnets. Those of my analyses made on pure material 

 were compared with the analyses of pyrope and almandite garnets used 

 bv Ford ^ To these ten analyses I could thus add eight new ones, 



' W. E. Ford, A Study of the Relations existing between the Chemical, Optical and other 

 Physical Properties of the Members of the Garnet Group. Am. Journ. Sei. XL, 1915, p. 34. 



