Review of Recent Geological Literature. 265 
extreme to another in mineral composition. ‘The whole series,” accord- 
ing to Mr. Iddings, in kis summary of this investigation, “is character- 
ized by a variable amount of porphyritical quartz in rounded grains, 
which is very noticeable in some of the basalts. These quartzes are 
primary secretions or crystallizations from the molten magma, and ex- 
hibit no definite relation to its chemical composition, being present in or 
absent from rocks of similar chemical composition. Their production 
is to be referred to certain physical conditions attending some earlier 
period of the magma’s existence. From analogy with the occurrence of 
iron olivine in rhyolitic obsidian, it seems probable that the formation 
of primary quartz in basalt took place through the influence of water- 
vapor while the magma was under considerable pressure ” 
On a late volcanic eruption in Northern California, and its peculiar lava. 
By J.S. Dinuer. pp. 33; with seventeen plates, and four figures in the 
texf. (Bulletin No. 79, U. S. Geol. Survey, 1891. Price, 10 cents.) 
Basalt enclosing abundant quartz grains, closely like that described by 
Mr. Iddings in the Tewan mountains, is found by Mr Diller to have 
been very recently erupted at the Cinder Cone, ten miles northeast of 
Lassen peak in northern California. An explosive eruption, ejecting 
bombs, lapilli, and volcanic sand, formed this cone about two hundred 
years ago, as shown by trees whose dead trunks still project through the 
lava that flowed out from the base of the cone before the explosive ac- 
tion ceased. Afterward a period of inactivity probably lasted a century 
or more, as shown by like deposits which overlie the volcanic sand and 
are covered by a second lava flow. The eruption of this latest lava oc- 
curred probably somewhat more than fifty years ago and was not accom- 
panied by any explosive ejection of fragmental material, the cone being 
undisturbed except at the point on its side whence the molten lava is- 
sued. 
The Cinder Cone rises very steeply to a hight of 640 feet and has an 
average diameter of 2,000 feet at its base and 750 feet across its top, be- 
neath which the pit of its crater sinks 240 feet. The later lava, occupy- 
ing an area three miles long and having an average thickness of nearly 
a hundred feet, was extremely viscous at the time of its eruption, and 
its cooling crust was repeatedly broken up by the moving mass beneath. 
Its surface therefore is composed of sharp, angular blocks, loosely piled 
together, which were shoved along as a huge stone pile. 
The explosively ejected fragmental lava of the earlier eruption and 
both ‘the earlier and later lava flows contain quartz grains, which 
frequently are so large and abundant as to give a porphyritic structure, 
though more generally they are small and inconspicuous. Their aver- 
age diameter is about one-thirtieth of an inch, but very rarely they are 
found over an inch in diameter. All of them have been greatly modi- 
fied, apparently by the corrosive action of the magma, and each grain is 
encircled by a shell of granular, acicular augite, which is separated 
from the quartz by a film of glass. The author concludes that the 
quartz became crystallized in the magma before its eruption. 
