1188 The American Naturalist. [December, 
ined critically. He proposes a classification based upon slight differ- 
ences in structure and appearance, ascribed primarily to differences in 
the conditions under which the rocks were formed, and consequently 
upon their geological age. They are divided as follows : 
PALEOZOIC TO CARBON. MESOZOIC TO TERT. TERT. TO RECENT. 
Granular Diabase Melaphyre Basalt 
Porphyritic Diabase-porphyrite Melaphyre-porphyrite Basalt-porphyrite 
Glassy iabase-glass Melaphyre-glass Basalt-glass 
It is also suggested that further definiteness might be obtained by 
prefixing the name of the characteristic phenocryst to the second por- , 
tion of the name of the porphyrites, and to the first part the name of _ 
the characteristic mineral not porphyritically developed. Thus olivine- 
diabase-augite-porphyrite is an olivine diabase containing porphyritic 
crystals of augite. Of the two theories proposed for the explanation 
of the variolite of Durance, the one regards the rock containing the 
peculiar -structure as related in some way to gabbro, the other looks 
upon it as an endormorphous contact product of diabase Mr. Cole * 
has examined the field relations of the rock, and has come to the con- 
clusion that the variolite is a devitrification product of a spherulitic 
tachylite occurring occasionally on the sides of diabase dykes, but 
more frequently on the surfaces of lava flows. According to this view 
variolite stands in the same relation to the basic lavas as pyromeride 
does to those of acid character. The author compares the conditions 
yielding the variolites with those surrounding the Hawaiianlavas. In- 
cidentally he mentions that gabbro is not as abundant a surface rock 
in the vicinity of Mt. Genévre as has heretofore been supposed. The 
serpentines of the region he regards as having been derived from some 
more basic rock than this, The age af the diabases and the associated 
variolites is supposed to be Postcarboniferous. Compound spheru- 
lites consisting of groups of small spherulites occur in a black obsidian 
at Hot Springs, in California. The compound body is marked by a 
divergent structure, which is due to a secondary crystallization set up 
in the rock after the small spherulites had accumulated at given points 
to form ıhe compound body. The radiating substance is thought by 
Mr. Rutley® to be orthoclase, crystals of which run uninterruptedly 
through the smaller spherulites. Mr. Rutley supposes the primitive 
spherulites to have been formed in the obsidian while it was still 
* Quar. Jour. Geol. Soc., May, 1890, p. 295. 
5 Ib., Aug., 1890, p. 423. 
