168 General Notes. 
one case, howeyer, where a dyke cut sandstone, it was noticed that 
biotite plates were developed parallel to the sedimentary planes of 
the sandstone, while muscovite formed perpendicular to these planes. 
The remainder of the paper is devoted to a discussion of the upper 
members of the Karroo formation and to the Pleistocene deposits, 
Another interesting paper is by K. Dalmer,’ on the quartz 
trachyte of Campiglia, in Tuscany. The glassy variety of this quartz 
_trachyte is a fine-grained gray rock, consisting of a glassy ground- 
mass in which are porphyritic crystals of sanidine, quartz, biotite and 
cordierite, with occasional crystals of plagioclase. The quartz grains 
all possess a rounded outline in cross section, and are surrounded by 
a zone of glass. In addition to the minerals mentioned above there 
also occur in this variety prismatic crystals of some member of the 
scapolite group light red garnets, apatite and zircon. In a felsitic 
variety scapolite is lacking. In the neighborhood of the quartz 
grains the felsitic groundmass of the rock is replaced by a zone of 
glassy material. The cordierite is less fresh and it is in the glassy 
variety, and in many instances is entirely replaced by pinite. In 
a third variety, occurring in dykes, the groundmass is completely 
crystalline. These dykes of grano-porphyritic trachyte were 
regarded by Lotti’ as quart porphyries, and as apophyses of a so- 
called granite mass which occurs about fifteen hundred metres 
distant from them. This mass was likewise examined by Dalmer, 
who, while he finds it to possess the characteristics of a granite 
porphyry, believes that its present condition is due to the conditions 
under which it cooled, and that the three trachytes and the granite 
porphyry are all portions of the same magma, which, from the 
nature of its surroundings, gave rise to rocks which from their 
structure and mineralogical composition must be classified under 
different heads. 
Professor ©. R. Van Hise? communicates some additional‘ 
notes on the enlargement of hornblende and augite in frag- 
mental and eruptive rocks. In the altered diabases of the Penokee- 
Gogebic Iron-Bearing Series crystals of uralitized augite are seen to 
have attached to them long acicular crystals of a very light green 
hornblende, which extend out from the uralite even into the sur- 
rounding decomposed feldspars. In other cases unaltered augite is 
surrounded by an almost sinuous sheet of amphibole. In both 
cases the crystallographic axes of the two minerals coincide. Dr. 
G. H. Williams® describes the alteration of ilmenite into rutile, in 
altered diabase from the vicinity of Quinnesec, Mich. Irregularly- 
shaped pieces of ilmenite are surrounded by a network of little 
prismatic crystals of rutile. 
1 Neues Jahrb. f. Min., ete., epi ii., p. 206. 
s Atti della Societa Toscana. Vol. vii. 
. JO 
me . . 
5 Neues Jahrb. f. Min., etc., "1887, ii. P 263. 
