1074 The American Naturalist. [Novembet, 
orientation is accepted the relations are not apparent. The paper is 
important as affording strong argument for a change in the position of 
crystals of hornblende and augite, as also for the interesting announce- 
ment of the discovery of a secondary augite. The parting of cer- 
tain hornblende crystals from St. Lawrence County, N. Y., analogous 
to the basal parting of augite, has been found by Williams" to be the 
result of twinning along gliding planes parallel to the face usually re- 
garded as the orthodome. Since the parting in augite takes place 
. parallel to the basal plane, and since in parallel growths of hornblende 
and augite the partigg in the two minerals is parallel, it is suggested 
that in both cases the plane parallel to which the parting takes place 
be taken as oP. The advantages of this new position lie in the cor- 
respondence between the morphological and optical properties of the 
two minerals. Crystals of beautiful blue ceZesz/fe are described by 
Williams? from the Helderberg Limestone in the western flank of 
Knobly Mountain, Mineral County, West Virginia. They occur in 
flattened lenticular pockets, partially or entirely filled with clay. The 
crystals, which are associated with gypsum and calcite, are found im- 
planted on the walls of the cavities or imbedded in the clay. The 
celestite is pyramidal in habit in consequence of the predominence of 
the brachypinacoid P4. In some crystals these faces occur alone, 
when the crystals are often rounded into lenticular bodies, Other forms 
observed are œ P=, 1P, oP, Pz;,and œP. oP is rough and drusy, 
and æ P= is vertically striated. The optical angle is 2 Vna = 49° 54; 
and composition almost pure SrSO, The resemblance in habit be- 
tween these celestites and thinolite, and their similarity with the San- 
gerhausen pseudomorphs that have generally been referred to gaylussite, 
are striking.——Becke 4 has examined some highly modified dolomite 
crystals from the Binnenthal and from Scaleglia, and magnesite from 
the latter locality, and on the former has found some new rhombohedra. 
The dolomite from Scaleglia is marked by unsymmetrical etched 
figures that differ in shape from those artificially produced on this 
mineral. The magnesite is interesting, as it contains two orders of 
scalenohedra, the first forms of this kind found on the mineral. 
hemihedral crystallization of calcite, siderite, and magnesite, and the 
tetratohedrism of dolomite are explained in accordance with t 
Sohncke-Wulff theory, by the fact that the latter's molecule comprises 
1 Am. Jour. Sci., May, 1890, P- 352. 
12 Ib., March, 1890, p. 183. 
18 Dana. Bull. U.S. Geol. Survey, No. 12, 1884. 
M Miner. u. Petrog. Mitth., X1., 1890, p. 223. 
