604 The American Naturalist. [July, 
there are here three independent volcanic centers, represented respect- 
ively by Ischia, Vesuvius and Mt. Nuovo. That they are on different 
volcanic fissures is indicated by the differences in the character of the 
lavas extruded from them, especially in their sodium and calcium con- 
tents. Ateach center each magma became differentiated, and this dif- 
ms geui explains the variety of the rock types discovered in each. 
study in the consanguinity of eruptive rocks' is the title of an 
article by Derby" in which is shown the fact that the occurrence of the 
eleolite syenites, phonolites, monchiquites and other related rocks in 
Brazil, point to the correctness of the notions of differentiation and 
consanguinity as explanatory of the existence of different phases of 
eruptive rocks within the same volcanic sphere. The author also shows 
that, while not having formulated the theory, its principle has been 
the guide in his work on the Brazilian rocks. 
Miscellaneous.—Upon examining spherulites of lithium phos- 
phate between crossed nicols, McMahon" finds that some of the group- 
ings present apparently miaxial crosses which remain fixed in position 
during a complete revolution, while in others the cross breaks up into 
two hyperbolic branches resembling those of biaxial optical figures. 
The phenomenon, the author regards as due to molecular strains that 
affected the spherulites at the time of their crystallization. 
Jour. Geol., Vol. 1, p. 579. 
"Mineralogical Magazine, X, p. 229. 
