1038 The American Naturalist. [December, 
General Notes. 
m 
PETROGRAPHY.' 
The Sioux Quartzite of Iowa.—The Sioux quartzite has long 
been known as the oldest sedimentary rock in Iowa. It has recently 
been studied by Beyer.” It is a white or red vitreous rock with which 
is associated a8 its upper extension a series of mottled reddish or pur- 
plish-black slates. The quartzites present the usual aspects of indu- 
rated sandstones. The constituent quartz grains are rich in ‘ quartz- 
needles’ which can be traced directly into rutile spicules. The slates 
are arenaceous. They exhibit no traces of slaty cleavage, though in 
some cases their quartz grains and micaceous constituents are distorted 
in such a way as to testify to a horizontal movement in the rock mass 
containing them. All the slates are mottled by spheroidal masses of 
a lighter color than the body of the rock. These masses are spheroidal 
with the longer dimensions of the spheroids in the bedding planes of 
the shale. Their lighter color is supposed to be due to the removal of 
iron from those portions of the rock they occupy. Associated with the 
quartzites is a great mass of olivine diabase consisting of a coarse 
grained aggregate of Jabradorite and oligoclase zonally intergrown, 
olivine, augite, biotite, hornblende, apatite and magnetite. Most speci- 
mens are much altered, the components having been changed into the 
usual secondary substances common to diabase. In structure the rock 
varies from the ophitic, in which the plagioclase is older than the 
augite, to the gabbroitic, in which the augite is the older mineral. 
An analysis gave: 
SiO, TiO, Fe,0, FeO Al,O, CaO MgO K,O Na,O H,O P,O, Total 
42:85 tr 13.66 20.23 6.85 3.42 1.90 5.78 .88 tr —100.57 
The Peridotites of North Carolina.—In connection with a dis- 
cussion of the occurrence and origin of corundum in North Carolina, 
Lewis’ gives us an interesting account of the basic rocks associated 
with the gneisses in that portion of the Appalachian belt included with- 
in the limits of the State. These basic rocks, consisting mainly of 
1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
? Iowa Geol. Survey, Vol. VI, p. 69. 
3 Bull. No. 11, North Carolina Geol. Survey, 1896. 
