1896.] Geology and Paleontology. 817 
to which it refers has e changed from its original character through 
devitrification. 
Mica-Syenites at Rothschonberg.—Two dykes of mica-syenite 
cut the phyllite formation near Rothschönberg, Saxony, producing in 
the neighboring rocks contact metamorphism. One of the dykes weath- 
ers spheroidally, and in the kernels of the spheroids fresh material for 
study was afforded Henderson, who found the rock to be composed of 
orthoclase, plagioclase, quartz, biotite, apatite and several accessory 
components. The feldspar and quartz both occur in grains and in 
crystals, the biotite in flakes. An analysis of the rock gave the figures 
below (I). 
The second occurrence differs little from the first. Muscovite is pres- 
ent as well as biotite, otherwise the two rocks are practically alike in 
mineral composition. Its chemical composition is shown in (II). 
SiO, Al,O, Fe,O, CaO MgO K,O Na,O H,O CO, S Total 
- I. 61.40 16.66 7.46 2.08 3.65 2.938 4.75 .76 154 .20—=101.43 
II. 57.63 16.47 5.87 5.25 4.44 3.12 5.15 .45 2.14 .95—100.97 
The structure of both rocks was panidiomorphic, although the develop- 
ment of secondary quartz renders them now hypidiomorphic. They 
are syenitic aplites. In the neighboring phyllites new biotite has been 
abundantly developed and hornblende has been produced in some 
quantity. The free silica which is abundant in the unaltered phyllites 
has become combined with metallic elements in the altered forms. 
While the percentage of silica in specimens taken at 2 meters and 11 
meters from the contact and at the contact is the same, the free quartz 
in the first is 43.38 per cent of the rock’s mass, in the second 38.94 per 
cent and in the third 34.06 per cent. 
GEOLOGY AND PALEONTOLOGY. 
Cambrian Rocks of Pennsylvania.—During the years 1892 
and ’93, Mr. Walcott made an examination of the rocks of Cambrian 
southeastern Pennsylvania for the purpose of determining whether the 
lower quartzites with their superjacent limestones were of the same 
geologic age, in the areas included between the Potomac and Susque- 
hanna and the Delaware and Susquehanna Rivers. The results of his 
work are published in bulletin form by the U. S. Geological Survey. 
ê Zeits. d. geol. Ges., XLVII, p. 534. 
