Foreign Notices in Mineralogy, &e. 31 
served any joints parallel to more than four of the planes of 
the rectangular prism, I consider the right rhombic prism as: 
the primary form. ‘The angles of this prism are 95° and 
85°; the planes which give the angle of 95° appear on ma- 
ny of the crystals as a “dihedral termination to secondary 
forms, analogous to some prismatic varieties of sulphate of 
barytes. The crystals are generally very minute, and ap- 
pear sometimes in small bunches, radiating from their com- 
mon point of attachment to the matrix. 
Besides the cleavages parallel to its planes, the rhombic 
prism divides also in the direction of its shortest diagonal, 
and its height is to the edge of the base as 2 to 1. 
The fact that presents itself to our notice here, of so dis- 
tinct a difference of crystalline form, produced by a change 
in the proportions only of the elements of the crystallized 
body, will tend to confirm the intimate relation that subsists 
between the chemical and crystallographical characters of 
minerals; and it appears to disprove M. Beudant’s conjec- 
ture, that only the secondary form of crystals are affected 
by a change in the proportions of their constituent chemi- 
cal elements. 
-Itis remarkable, too, that lead should alone present so 
many instances of a single base combining at the same time 
with two acids. 
London, 13th May, 1820. 
From No. 6 of Edinburgh Philosophical Journal. 
© New works on Petrifactions.—1. The well known ge- 
ologist, Baron Von Schlotheim, is just about to publish : an 
extensive work on petrifactions, and, judging from the ac- 
curacy, and extensive knowledge of the author, it cannot 
fail to prove a valuable addition to this interesting branch | 
of natural history. 2. Emmerling, the Mineralogist, has 
also announced a work on the fossil organic remains met 
with in brown coal, and other new formations of the same 
description. 3. There has just been published at Leip- 
zig, a work in folio, with numerous plates, entitled Geog- 
nostical Flora of a former world, by Graf Kasper Von 
Sternberg. From the plates of this work, sent to the Wer- 
nerian Society by Count Banos, the drawings appear to 
be faithfully executed, and many of the cbjects represented 
