18 GEOLOGICAL MEMOIKS. 



The continental equivalents are next discussed in the same order, 

 as follows :■ — (I.) Portland Limestone, or Zone of Trigonia gihbosa ; 

 (II.) Lithographic limestone of Solenhofen ; (III.) Zone of Pterocera 

 Oceani and Ammonites mutabilis ; (IV.) Astarte-limestone and Zone 

 oi Ammonites tenuilobatus ; (V.) Zone of Cidaris Jlorigemma and Am- 

 monites bimammatus. Dr. Waagen also says a few words on the con- 

 tinental representative of the Lower Calcareous grit, which he be- 

 lieves to exist in the north of France ; but he remarks that the 

 further one goes southward the nearer do beds apparently of this age 

 approximate to the " Transversarius-zoue," and in the Dep. Cote 

 d'Or there is the fii'st appearance of the Scyphia-limestone on this 

 horizon. But the point to which he especially draws attention is 

 that a " Corallien " formation occurs at all the horizons of which he 

 treats. The preceding detailed Table, translated from Dr. Waagen's 

 pamphlet, gives his conclasions on this head as fully as possible, so that 

 it is unnecessary to go further into the subject, except to quote his re- 

 mark that " The ' Corallien ' extends through the whole tipper Jura ; 

 where it is distinguishable it occurs at the expense of either the Ox- 

 ford or the Kimmeridge Group, and to preserve these two formations 

 intact I sacrifice the ' Corallien.' The boundary between the Oxford 

 and the Kimmeridge Groups falls between the beds with Cidaris 

 Jlorigemma (or the zone of Ammonites bimammatus) on the one side, 

 and the Astarte-limestone (or the zone of Ammonites tenuilobatus) on 

 the other side ; therefore, from the lower boundary of the zone of 

 Ammonites tenuilobatus upwards we have, in South-western Germany, 

 not Oxford but Kimmeridge beds." [J. M. & H. M. J.] 



Chemico-mineealoqical Eeseaeches on the Felspaks. - 

 By Dr. Gustav Tschekmak. 



[Chemiscli-mineralogisehe Studien. Von Dr. Gustav Tschermak. I. Die 

 Feldspathgi'uppe. Sitztmgsbericlite der k.-k. Akad. der Wissenscli. zu Wien, 

 Math.-nat. Classe. Band. 1. Erste Abtheilimg. Heft V. Jahrg. 1864, pp. 

 566-613, 2 plates.] 



HiXHEETO it has been considered that the species of Felspar were 

 very numerous ; but the author of this paper believes that, with the 

 exception of Hyalophane and Danburite (both of rare occurence), 

 they may all be resolved into mixtures of three true species, or 

 genera (Gattioigeoi), as he terms them — namely, those known in the 

 pure state as Adularia, Albite, and Anorthite, hose knsh-. Soda-, 

 and Lime-felspars. The Potash-felspars he considers to be the re- 

 sult of regular alternations of Orthoclase with Albite ; and the other 

 Felspars to be isomorphous mixtures of Albite with Anorthite, some- 

 times with small quantities of Orthoclase. Oligoclase, Andesiae, and 

 Labradorite appear to be merely members of a great series, in which 

 many transition-forms occur. The cause of the partial isomorphism 

 of Orthoclase and Albite, of the more complete isomorphism of 

 Albite and Anorthite (as well as Danbuiite), and finally of Adularia 

 and Hyalophane, lies in their similar atomic constitution, as they 

 possess corresponding atomic formulae, which are given by the author 

 as foUows : — • 



