HORNES SANDLING FOSSILS. LEYDOLT — CRYSTALS. 23 



On the Gasteropoda a7id Acephala of the Sandling Marble. 



By Dr. M. Hornes. 



[Proceedings of the Imperial Academy of Sciences, February 15, 1855.] 



This is a notice by M. Hornes oa the Gasteropoda and Acephala 

 discovered in the Marble beds of SandHng, near Anssee, by Dr. Fis- 

 cher, Physician to the Duke MaximiUan of Bavaria. The Cephalo- 

 pods occurring in the analogous strata of Hallstatt have been described 

 by M. von Hauer*, the Corals by M. Reussf, and the Brachiopods 

 by M. Suess;];. The other molluscs of this Fauna, however, were but 

 very little known before Dr. Fischer had recently succeeded in ex- 

 tracting from this hard marble 30 species of molluscs, nearly all 

 previously undescribed, and one of them being the type of a new 

 genus, named Platystoma by Hornes. 



The fauna of this group, comprising about 70 species of Cepha- 

 lopods (among them are some of gigantic size), bears a peculiar 

 facies, quite distinct from that of any extra-Alpine European deposit. 

 Some forms resemble palaeozoic types, whilst others exhibit a de- 

 cidedly Jurassic character. The Hallstatt and Sandling limestones 

 present a distant resemblance to the St. Cassian series, and, like the 

 latter, may be supposed to be a local deposit confined to the Alpine 

 district. [('ount Marschall.] 



On the intimate Structure of Minerals, as exhibited by the 

 action 0/ Hydrofluoric Acid. By Prof. Leydolt. 



[Proceedings of the Imperial Geological Institute of Vienna, December 12, 1854.] 



In this communication Prof. Leydolt gave an explanation of the 

 method which he had invented to demonstrate the intimate structure 

 and composition of crystallized and non-crystallized inorganic sub- 

 stances by submitting them to the corrosive action of diluted Hydro- 

 fluoric Acid ; the planes and cavities produced by the action of this 

 menstruum on the surface of the substances submitted to it being 

 immediately connected with the crystallographic system to which 

 they belong, and with the position of the axis. 



Prof. Leydolt exhibited several varieties of Rhombohedric Quartz 

 treated in this manner. Complete crystals of this mineral, which 

 had been exposed to the action of the acid, show on the edges of 

 their hexagonal pyramids small planes, situated sometimes on their 

 left, and sometimes on their right side. These planes, produced on 

 plates cut perpendicularly to the crystallographic axis, may be sub- 

 servient to the recognition whether any crystal of quartz is a binary 

 combination of two individuals turning right or left, even when no 

 difference is to be discovered by investigation of the optical phseno- 

 mena. Prof. Leydolt has applied to the etched surfaces produced 

 by his mode of operating the method invented by Sir David Brewster 



* See above, p. 22. f Ibid. 



X See the Anniversary Address, in this No., p. Ixvi. 



