38 The American Naturalist. [ January, 
opment of crystallized specimens. This mode of illustration can 
hardly be carried too far to suit the taste of the professional mineralo- 
gist, but as it involves expense and time in the preparation of the cata- 
logue, we would suggest that the particular combination exhibited by 
a crystal might nearly as well be indicated by the use of form sym- 
bols. The sixteenth edition of English’s catalogue contains a classified 
list of mineral species arranged like that in Dana’s “System” (6th 
Ed.), in which is given after each species the symmetry, hardness, spe- 
cific gravity, and chemical composition. A supplement to the list 
includes the species mentioned in Dana’s supplement as well as min- 
erals of more recent description. The book is quite free from errors and 
contains an alphabetical index. Only about one-third of the book is 
devoted to advertising. . 
Leadhillite from near Granby, Missouri.—The rare mineral 
leadhillite occurs near Granby, Mo.,in part in good crystals associated 
with massive cerussite. As studied by Pirsson and Wells’ these crys- 
tals are either prisms or plates having dimensions of one or more cen- 
timeters. The symmetry is monoclinic and pseudo-hexagonal, and the 
combinations are simple, usually (001), (110) and (100), more rarely 
also (201), (414) and (418). -Twinning parallel to the unit prism is 
common and the basal cleavage is perfect. The physical and optical 
properties agree in the main with those of the already known leadhill- 
ite. The etched figures on the base (dilute nitric acid) closely resem- 
ble those of the micas. An analysis gave the following results: 
SO, CO, FO BO Total 
733 814 8244 1.68 - 99.59 
The formula for the mineral is therefore Pb SO, 2Pb CO,. Pb 
(OH),, which does not agree with any of the other published analyses 
of the mineral but is the formula which has been suggested by Groth. 
Two New Instruments for Mineral Study.—Tutton® has 
published a brief preliminary notice of two important instruments 
which he has deyised, full descriptions of which will be printed in the 
Philosophical Transactions. One of these is a delicate instrument for 
grinding very accurately in any desired direction, prisms and sections 
of minerals for optical study. In half an hour the two surfaces of 
the section may be pripara. The method is specially cay diet to cut- 
5 Am. Jour. Sci., xlviii, pp. “219-226, Sept., 1894. 
¢ Proc. Roy. Bas ly, (1894), pp. 108-113. 
