238 
The American Geologist. 
April, 1896 
charoidal can be seen on the cut surface of the specimen from 
which the thin sections were taken. 
Group 2. Glass, with inclusions. This is quite abundant. 
In some cases in the mounted thin sections the little olivines 
seem to swim idiomorphically in this glass. In others it is 
crowded with hundreds of black octahedra whose nature is 
unknown. 
Group 3 (and possibly groups 5 and 6). Asmanite (tridy- 
mite). By the kindness of Prof. A. Lacroix samples of the 
tridymite of the Breitenbach meteorite have been compared 
with the grains represented by this group. In conchoidal 
fracture surfaces, in cleavages and in double refraction the 
two are identical. They are equally similar to the tridymite 
of Rocher du Capucin. 
Group 4. An unknown substance which has a bisectrix 
np (a) and an optic angle of 10° to 15°. The black cross 
hardly becomes distorted on rotation. The characters assigned 
t° maskelynite by Tschermak do not apply to these grains 
very well in respect to their general outlines, nor in respect to 
their resemblance to plagioclase.* In making a Boricky test 
of the grains of the mixed powder those of group 3 remained 
undissolved. The only crystallites that were formed were bi¬ 
axial and indicated lime, or lime and magnesia. No soda nor 
potash was found in the test made. In the absence of cleav¬ 
age, only, does group No. 4 resemble maskelynite, while in the 
peculiar and only partial double refraction, group No. 5 re¬ 
sembles maskelynite as defined by Tschermak. 
Paris , Jan., 1896. 
[To be continued .] 
EDITORIAL COMMENT. 
Glacial Lakes of the St. Lawrence Basin. 
Quite diverse opinions have been held concerning the na¬ 
ture of the bodies of water which formed the Late Glacial or 
Champlain shore lines in the St. Lawrence basin, ranging in 
hight, in different portions of the region, from a few feet up 
to more than 600 feet above the present great Laurentian 
*The characters of maskelynite and of tridymite are summarily stated 
by Cohen in his recent work, Meteoritenkunde , Stuttgart, 1891. 
