1896.] Petrography. 661 
pieces several feet in diameter. These are cemented together by finer 
portions of the same substances, among which have been deposited zeo- 
lites, carbonates, opal and other secondary minerals. Some beds of 
this tuff are so filled with large fragments of basalt, tephrite, ete., that 
the rock composing it has been called the “ Brocken Tuff.” Itis to 
the study of the fragments in this tuff that Graber’s paper is devoted. 
The basalts and tephrites constitute sheets and lava streams that are 
interstratified with the tuffs and sediments. Among the former rocks 
are noticed feldspathic, leucitic and nephelinic varieties, besides in 
several places magma-basalts. In addition to sheet basalts, dykes and 
chimneys of this rock have also been observed. 
The rocks in all their forms are normal in their development. The 
author regards contact action around the chimneys as the safest crite- 
rion by which to distinguish these forms from denuded sheets and 
flows. The tephrites comprise hauyn-tephrites, in which hornblende 
and aegerine are present, nepheline-tephrite, including trachytic and 
andesitic varieties, and leucite-tephrite composed of phenocrysts of 
augite, plagioclase and grains of magnetite in a groundmass of these 
same components, and leucite, biotite and nepheline. 
The augite consists of two generations of magnetite and augite in a 
glassy base. Its analysis gave: 
SiO, TiO, P,O, Al,O, Fe,O, FeO CaO MgO K,O Na,O H,O Moisture Total 
43.35 1.48 1.54 11.46 11.98 2.26 7.76 11.69 .99 3.88 241 59 ==99.34 
The feldspathic basalt and the andesitic tephrite are the only rocks 
that seem to have affected the sediments with which they are in con- 
tact. Quartzites are changed to aggregates of quartz grains in a glass 
matrix, where the action is not extremely severe, and to an aggregate 
of interlocking quartz grains where it has been intense. The article 
closes with an account of the detailed results of analysis of ten speci- 
mens of the voleanic rocks. 
Graber’s article is devoted principally to a description of the frag- 
ments found in the Brocken-tuff. These are all tephritic rocks, among 
which andesitic, leucitic and phonolitic types are recognized. The 
characteristics of the components of all these types are portrayed in 
great detail, especial care being given to the descriptions of the augite 
and the plagioclase. The phonolitic tephrite is characterized by the 
presence of nosean, which is in irregular grains, In the andesitie teph- 
rite, which is the most basic variety, the porphyritic augite has an ex- 
tinction angle cA C of 58°-62°, in the leucitic type its extinction is 
