1890.] Mineralogy and Petrography. 1189 
liquid, and then to have floated around until they aggregated. After 
the formation of these accumulations they began to crystallize, and 
this produced the radiating structure. Mr. Iddings, who has also seen 
the specimens, regards the radiating structure as original and the 
spherulitic structure as secondary. The bodies, he thinks, are litho- 
physe, and not spherulites. The hornblende-bearing rocks of the 
Prussian Graftschaft Glantz have been divided into two groups,—the 
first comprising eruptive syenites, and the second including hornblende 
schists. Traube® believes that the rocks of both groups are but facies 
of the same mass, but whether eruptive in origin or belonging jo the 
crystalline schist series he is unable to decide. Both the so-called 
' syenites and the hornblende schists consist of orthoclase, quartz, mica, 
and augite, together with hornblende derived from it. The amount 
of the hornblende present (all of which is secondary) and of the other 
constituents varies so widely that intermediate varieties between the two 
types are quite common. ‘The rock in all cases is an augite-gneiss or 
a quartz-bearing augite-mica-syenite, From the nature of certain phe- 
nomena observed in limestone in contact with the hornblende rocks 
it is thought possible that these latter are eruptive. In a very short 
communication Dr. Hobbs? gives an account of the alteration of 
gabbro into hornblende-gneiss through gabbro-diorite at Ilchester, Md. 
The change from gabbro into gabbro-diorite is similar in its essentials 
to that described by Williams in the Baltimore area. The change into 
gneiss is effected through the granulation of feldspar, the fraying-out 
of hornblende, and the production of epidote and quartz. Pilot 
Knob, a hill seven miles southwest of Austin, Texas, is regarded by 
Prof. Hill as a Cretaceous volcano. Its material, according to Mr. 
Kemp, consists of nepheline-basalt, with phenocrysts of olivine and 
augite in a ground-mass of microlites of augite and grains of magne- 
tite in a nepheline-glass. 
Mineralogical News.—/JVew AMinerals.—Rammelsberg ? has dis- 
covered associated with the eudialyte of Sigteró, near Brevig, in Nor- 
way, a new feldspar, which he calls szgzezzfe. It has the cleavage 
of orthoclase, Its extinction against the edge oPA»P& is 16°. 
n oP two sets of twinning lamelle make with each other angles of 
7°-9°. The extinction of each individual is therefore 315?—412?. 
An analysis, corrected for impurities, gave: SiO,—50.27 ; Al Kar 
5 Neues. Jahrb. f. Min., etc., 1890, I., p. 95. 
t Trans. Wis. Acad. Sci., etc., VIIL., p. 155. 
8 Amer. Geol., Nov., 1890, p. 292. 
9 Neues. Jahrb. f. Min., etc., 1890, II., p. 71. 
