312 MINERALOGY. 



over the crystals is variable. He has not been able to deduce from his 

 studies any very complete system, and the results are therefore rather 

 wearisome in their details. 



The optical properties of isomorphous mixtures have been studied by 

 Wyrouboff, and Mr. C. Dolter has digested all the analyses of the min- 

 erals of the pyroxene family, and also studied thei r physical characters. 

 As a result he has given a classification of the varieties of this mineral, 

 which contains some improvements. 



Mr. E. Mallard has issued the first volume of his treatise on geomet- 

 rical and physical crystallography, accompanied by an atlas of nine 

 plates. The completed work is to cover the field of mineralogy, and is 

 of much importance, since no very extensive general treatise on miner- 

 alogy has appeared in France since the time of Hauy. 



Prof. J. Eeinhard Blum, in his old age, has added a fourth supple- 

 ment to his work upon pseudomorphs. The better part of his life may 

 be said to have been devoted to this study. His work has become one 

 of the classics of mineralogy, and has had much influence in geology. 

 He evidently intends that so long as he lives his work shall be kept 

 abreast of the times. If he is not longer able to take part in the active 

 hard work that is being devoted to this subject, his new supi)lement 

 shows that nothing of importance escapes his attention or overtasks bis 

 memory. 



