1048 General Notes. [ December, 
cation has recently been published by Heath & Co., of Boston! 
It is a neat little book of thirty-five pages, intended primarily to 
call the attention of teachers to the rise and development of the 
youngest branch of geological science, and to the methods which 
are made use of in it. A very large amount of information relat- 
ing to the history of petrography is embraced within the first 
twenty-five pages of this little volume. The next five pages con- 
tain a list of the most important works devoted to the subject and 
the periodicals in which petrographical articles are published. In 
the remaining pages the methods made use of in the preparation 
of thin sections are described and the names of reliable dealers 
in the instruments and materials used, with the cost of these, 
given. 
MINERALOGICAL News.—Ptilolite? is a new mineral, described by 
Cross and Eakins, from Colorado. It occurs in the cavities of a 
vesicular augite-andesite found as fragments in the conglomerates 
of Green and Table mountains, in Jefferson county. It forms 
delicate tufts and spongy masses composed of short hair-like 
needles which are usually deposited upon chalcedony in the pores 
of the rock. Under the microscope these needles are seen to be 
colorless, transparent prisms about .oo1™™ in diameter, terminated 
by a basal plane. Their extinction is parallel to the prismatic 
axis. An analysis of the purified material yielded Mr. Eakins 
the following result: _ 
50, AO, œO KO N0 Ho 
70.35. 11.90 3.87 2.83 0.77 10.18 
- This corresponds to the formula Ro Al,O,, 10SiO, + 5H-0. The 
mineral is interesting as being the hydrated form of the most 
acid anhydride known among the silicates, with the exception of 
the rare mineral milarite. A pseudomorph of limonite after 
pyrite? recently found in Baltimore county, Maryland, con- 
tains six of the seven possible crystallographic forms of the 
regular system. The forms actually observed are O, 00%, . 
[=>]. [F] 202, and 30. The fact that only two planes of the 
forms |. 202, and 30 are developed in each octant imparts to 
the crystal an orthorhombic symmetry. The turquoise ph 
Los Cerillos, New Mexico, has been studied chemically = 
microscopically by Messrs. Clark and Diller,‘ of the United States 
Geological Survey. It occurs imbedded in a fine-grained re 
orthoclase rock with a microgranitic structure, sometimes 1? 
by G. H. Williams, 1886. r 
on and L. G. Eakins. Amer. Jour. Sci., XXXII, a 4 p kaii 
XXXIL, Sep., 1886, p: 211. 
N 
