Mineralogy and Geology. 405 
. Note to poy on soni eic.. p. 361; by the authors— When 
our r artic just going to press, we received a | etter from Prof. A. 
“Knop, aston Carlsruhe, oo 13th , directing our attention to his extreme- 
ly interesting paper, eitrdge zur Kenntniss s der Steinkohlen-Formation 
und des Rothliegenden im erzgebirgischen Bassin, Neues Jahrbuch fir 
Min., 1859, in which we find, p. 544, details of his investigation on - 
: crystallography of the Schneckenstein “Kaolin.” Prof, Baa op has 
ticipated our observations on this substance in good part, as one 
from the following quotation, “The crystals of the Kaolin rhe Schneck- 
enstein have dimensions admitting of measurement under the micro- 
scope. They have an average length of about 0-021 mm., and a breadth 
gles connected by the macrodiagonal. Here and there the crystal-plates 
are aggregated to rhombic prisms and exhibit, on ape assumption of 
Pand cP.0P.aPpa. 
“ee measurements gave constantly 118° for the obtuse ae of 
the plan 
The specimen from Schneckenstein kindly sent us by Prof. Knop, 
who first brought it to Wobler’s notice, perfectly resembles that received 
from Prof. Clark, as well as others adhering to topaz specimens from 
Schneckenstein in Prof. Brush’s collection. These crystals are, however, 
of the last named substance, drawn ie the camera lucida, the — 
tself, know as. Thonsies n or Pelsitup, i of close 
wines wens in “par well defined or peacoat in Scat position to mak 
ick packets, 
This rap agrees with what we have given of various clays, and 
wes te of two conclusions, viz., either the substance is impure kao- 
inite, or, if pholerite, the latter has an appearance and prismatic erys- 
tallization closely similar to kaolin 
ND SERIES, oe XLII, No. 129.—May, 1867. 
