52 Review of Recent Geological Literature. 
marvelous quaternary phenomeaa of the lo^-er cotton belt and of the 
great plains." 
The detailed results will be given in Prof. Hill's forthcoming report on 
the geology of south-western Arkansas. 
On the origin of primary quartz in basalt. By Joseph P. Iddings, of 
the U. S. Geol. Sur. (From Am. Jour, Sci,, Sept., 1888). This paper 
describes certain specimens of basalt which exhibit a remarkable number 
of porphyritic grains of quartz, recently collected in New Mexico, in the 
vicinity of the Rio Grande Canon . 
These quartzes are plainly not the product of alteration nor infiltration, 
for the rocks are fresh, and on the surface of the olivines but slight 
cliange is visible. Each grain is closely surrounded by a shell of augite 
crystals intimately connected with the enclosing rock mass. The quartz 
is pure and free from inclusions of gas, fluid or glass. Each grain is a 
single individual with uniform optical orientation throughout. They are 
not made up of an aggregate of small grains, the form which secondary 
quartz usually assumes. The grains are rounded or subangular. They 
are not like the quartzes of granites, gneisses and sandstones which are 
more or less permeated with inclusions of gas and fluid, but are like the 
porphyritic quartz grains of volcanic rhyolytes. 
The author mentions several other similar chemical occurrences that 
seem paradoxical under ordinary physical conditions of crystallization, 
such as an iron olivine in a rhyolyte with 75 per cent of silica and less 
than 2 per cent of iron oxide. He concludes that when such anomalous 
coincidences are found the surrounding physical conditions which attended 
the solidification of the magma must have been exceptional. The excep- 
tional physical conditions may have preceded the final solidification, and 
been of such a character as to demand the secretion and crystallization of 
the anomalous mineral forms, and indeed seem to have been so in the 
case of the quartzes, and to have ceased. This is evinced by the resorp- 
tion of the angles and edges of the crystals into the general basic magma, 
resulting in the rounding of the grains . 
After enumeratiag the various physical conditions and agents which are 
likely to vary within the crust of the earth, such as temperature, pressure, 
viscosity, water vapor, eutectic substances, and their combined as well as 
their separate action on the magma, he applies them to a hypothetical 
case in the production of known quartz-bearing basalt; and suggests that 
through the agency of absorbed water, acting under favorable conditions 
of pressure and temperature, a partial consolidation of the deep-seated 
magma may be effected in the production of extremely acid and basic 
silicate minerals in unstable solidification, the dissociating action of heat 
or of super-heated steam being sufficient to nullify the ordinary chemical 
affinities but not able to suspend the tendency to isolation and crystalliza- 
tion. On the removal of the exceptional physical conditions, the unstable 
solidification may be broken up and the crystals partially or wholly re- 
sorbed again into the general magma; or if final solidification supervened 
they may be embraced as indigenous though abnormal crystals in the 
resulting rock. The paper is a very interesting and valuable one to the 
petrographic student. 
