172 The American Naturalist. [February, 
* 
duced by the tendency of some carbonate to form concretionary mas- 
ses around grains of sand or small shells. The original carbonate has 
for the most part disappeared, leaving the magnetite as a pseudo- 
morph. Among the eruptives is a rock that the author calls eurite, fol- 
lowing d’Aubuisson,® although it would seem that the name quartz- 
keratophyre would sufficiently well characterize it. The rock is a 
bluish-gray compact substance with a specific gravity of 2.64. It con- 
tains quartz and feldspar crystals, wisps of biotite and spherulites of 
granophyre, more particularly around the porphyritic crystals, in a 
groundmass composed principally of a chloritic substance. Its analy- 
sis shows it to contain a soda-rich feldspar : 
SiO, ALO, FeO, MnO CaO MgO KO Na,O Loss 
TATI 13.70 3.42 tr. 1.94 OF 2.00 “4.93 1.08 
——In his description of the section Tanneberg of the geological map 
of Saxony, Dalmer? mentions two rocks of some interest. The first is 
a sericite-gneiss, composed of quartz, plagioclase and sericite, with a 
breccia-like structure produced by pressure. The quartz and plagio- 
clase are shattered, and the broken pieces are reunited by a cement of 
secondary quartz and sericite. The second is a chlorite-gneiss, con- 
sisting of orthoclase, albite, chlorite and quartz. This occurs in 
varieties of different degrees of coarseness. As it becomes finer in 
grain it loses feldspar, and assumes muscovite, until finally it approaches 
in structure and composition the phyllites of the region. Kendall § 
gives a list of the basic dykes on the island of Mull that contain the 
glassy selvages known as tachylite. It has been observed that the 
thickness’ of this glass band is always greatest in that portian of the 
dyke in contact with the most compact rock. A new type of tachylite, 
called by Groom? carrockite, is associated with gabbro at Carrock 
Fell in the Lake District, England. It consists of a green glass en- 
closing spherules of quartz, feldspar, and granular aggregates of augite, 
and porphyritic crystals of the same minerals.—Prof. Bonney” has ex- 
amined certain banded micaceous schists from Morlaix, Brittany, which 
he thinks are the result of pressure and contact action. The rocks 
were originally stratified sands and muds, that were crumpled and 
foliated by pressure, and in which a light and a dark mica, chiastolite 
and andalusite were developed. By the subsequent intrusion of gran- 

®Traité de Geognosie, 1819, p, Iry. 
7 Erl. z. Geol. Specialk. des Königr. Sachsen Blatt, 64., 
3 Geol. Mag., Dec., 1888, P- 555. 
® Geol. Mag., Jan., 1889, p. 43- 
10 Quart. Jour. Geol. Soc., Feb., 1888, p. 11. 
. 
