——a ————— 
Se eee 
1894.] Petrography. 799 
PETROGRAPY: 
In a long and extensive article, Miigge’ treats of the keratophyres of 
the Lennethal in Westphalia, and the neighboring regions, and their 
tuffs. The rocks have been considered as fragmental schists by some 
observers and as squeezed eruptives by others. They are known gen- 
erally as the Lenneporphyries. Miigge finds that some of them are 
genuine eruptives and some are the tuffs of these. The massive rocks 
are keratophyres and quartz-keratophyres, sometimes carrying large 
phenocrysts of quartz and feldspar and at other times free from these. 
The groundmass of the keratophyres is made up of bleached biotite, 
sericite, feldspar, opal and glass, with traces of spherulitic structure. 
Schistose varieties of the quartzose varieties have become foliated 
through pressure, as shown by the fractured quartzes and feldspars 
that occur so abundantly in them, the presence of lenticular areas of 
quartz mosaic and the greater abundance of sericite. The most char- 
acteristic of the lenneporphyries are tuffs in which the ash structure 
is very well exhibit. The typical tuff structure is described by the 
author as due to the accumulation of glass particles with concave 
boundaries. These are mingled with complete and broken crystals of 
various minerals and often with sedimentary material. Rocks com- 
posed of intermingled volcanic and sedimentary fragmental material 
the author would call tuffites; when metamorphosed, tuffoids. Many 
of the rocks in the Lenne district have suffered dynamic metamor- 
phism with the production of secondary quartz, feldspar, sericite, car- 
bonates and chlorite. They are, therefore, tuffoids. The new material 
was formed partially from the decomposition of the rock’s materials 
and partially with the aid of alkaline solutions originating outside of 
the metamorphised rocks. 
Nepheline-Melilite Rocks of Texas.—Osann’ finds a melilite 
nepheline basalt occurring as dykes in the Cretaceous of Uvalde Co., 
exas, and nepheline basanites forming buttes and hills in the same 
region. The basalts are typical melilite varieties, containing pheno- 
erysts of olivine and micro-porphyritie crystals of melilite with all 
the characteristic features of this mineral. Perofskite is a common 
' Edited by Dr. W. S. Bayley, Colby agerem Waterville, Me. 
*Neues Jahrb. f. Min., etc. B. B. viii, p. 525 
*Jour. Geol, Vol. I, p. 341. 
