176 Notices of Memoirs — Petrology. 



showed that it was closely related to polyhalite, and this relation 

 suggested to Zepharovich the specific name ((Tvj<yev^<;, related). 



Syngenite is a hydrous double sulphate of calcium and potassium, 

 containing CaKjSaOg.HaO (corresponding to the rational formula 

 CaO'SOg+KgO'SOs+HaO). Its crystals, though commonly affecting 

 a monoclinic habit, were originally described as rhombic, partly on 

 account of their optical characters, and j)artly because their forms 

 resembled those of the corresponding artificial salt, which was be- 

 lieved to be rhombic. The present paper describes in great detail 

 the crystallographic and optical characters of Syngenite, and the 

 author shows that both this mineral and the artificial salt must be 

 referred to the monoclinic system. 



The mineral recently described by Eumpf under the name of 

 Kaluszite seems to be identical with Syngenite. 



Zepharovich's paper is accompanied by figures of the principal 

 combinations exhibited by the crystals of syngenite, and by a stereo- 

 graphic projection of the poles of 21 observed planes. F. W. R. 



• 8 



PETEOLOGY. 



lY. — Microscopic ExaImination of some Pobphykites and Allied 

 EocKS FROM THE DISTRICT OF THE Nahe. Mikrosko.pische 

 Untersuchung einiger Porphyrite und verwandter Gesteine 

 aus dem Nahe-Gebiete. Yon Herrn Prof. A. Streng. Leonhard 

 u. Geinitz's Neues Jalirb. f. Mineralogie, u.s.w. 1873, Heft iii. 

 pp. 225-241. 

 OME time ago, Prof. Streng published the results of a micro- 

 scopic study of the rock called Palatinite, which occurs in the 

 Yalley of the Nahe, a tributary to the Ehine. In the present paper 

 he extends his researches to the other crystalline rocks associated 

 with the Eothliegende of this district, and describes in detail the 

 microscopic structure of the following rocks, namely — (1). A 

 Quartz-porphyry, from Miinster on the Stein. (2). An Orthoclase-por- 

 phyry, from the foot of the Unterhauser Berg. (3). A porphyrite, 

 from the southern foot of the Gienberg. (4). A grey porphyrite, 

 containing tridymite, from near the rail way -station of Waldbokel- 

 heim. (5). A brown porphyrite, from the same locality. (6). A 

 porphyrite, from the valley below Bokenau. (7). A dark porphyrite, 

 occurring in loose fragments in this valley. (8). A brownish-grey 

 porphyrite, from the same locality. (9). A quartziferous Palatinite, 

 from the foot of the Welschberg. 



These nine rocks fall into a natural series, having at one end a 

 quartz-porphyry, containing quartz, orthoclase, a triclinic lime-soda 

 felspar, and a little hornblende. By gradual diminution in the 

 proportion of quartz and orthoclase, a transition is effected, through 

 the quartziferous porphyrite, to the typical porphyrites, which con- 

 sist mainly of a lime-soda felspar and hornblende ; thence, by 

 addition of an augitic mineral and removal of hornblende, a rock 

 may be obtained with the composition of Palatinite, which there- 

 fore constitutes the final term of this series. E. W. E. 



