264. Abstracts of Foreign Memoirs. 
The ‘ Terrain & Chailles’ (so named by Thurmann on account of its 
containing siliceous particles, which are locally termed ‘Chailles’ ) 
is one of the inconstant minor subdivisions of the Middle or Upper 
Jura, and occurs in the Cantons of Basel, Solothurn, and Berne, as 
well as in the neighbouring French Jurassic area. It is rich in well- 
preserved fossil remains, more especially of Corals, besides Crinoids 
and Echinoderms, but Cephalopods are rare; the whole assemblage 
constitutes, however, a peculiar and very distinct fauna. Of the 
Echinoderms, the most important being Cidaris Blumenbachii, Ag. 
(C. florigemma, Phill.), C. cervicalis, Ag., Hemicidaris crenularis, 
Ag., and Glypticus hieroglyphicus, Ag., scarcely a single species is 
known to the author to occur on any other horizon. For this and 
other reasons, which are given by M. Merian in detail, he considers 
the ‘ Terrain & Chailles’ to be the equivalent of the Crenularis-beds 
(so-named by Herr Mésch, from the occurrence in them of the Hemi- 
cidaris crenularis, Ag.) of the ‘White Jura’ of the Canton Aargau, 
the above-named characteristic species of that formation occurring 
therein in company with Stomechinus perlatus, Desm., and Diplo- 
podia Annonii, Des. 
The position of the Crenularis-beds is shown in the following 
table of the Aargau Jura, the beds being given in descending 
order: — Proximate thickness. 
feet. 
11. Cidaris-beds : ‘ : : ae i 80 
10. Passage-beds (Grenzregion) : : : ; 9 
9. ‘Badew. beds ; ; : 3 ; ; { 45 
8. Letzi beds ; : F : : ; 32 
7. Coneretionary bed. : : : 109 
6. White Limestone ©. : : 2 4 10 to 12 
5. Caprimontana-beds . F é : : 20 
4, CRENULARIS-BEDS . : : 5 E 12 to 15 
3. Geissberg beds : : . . . 160 to 110 
2. Effing beds 4 : : : : : . 3800 
1. Birmensdorf beds. : : : ; ‘ 18 
Maximum total . . 650 feet. 
The Birmensdorf beds, forming the lowest member of the series, 
repose immediately on the Ornatus-clay,—the ‘Terrain Callovien’ 
of D’Orbigny. 
. ‘Ueber den Zwillingsbau des Quarzes’ (On Twin-crystals of 
Quartz), by Dr. Friedrich Scharff. With two Plates. In this paper 
the author discusses, at great length, the question whether twin- 
crystals of Quartz are really known to exist, and he comes to the 
conclusion that, while certain crystals, obtained from Floéha and from 
Munzig, appear to establish the fact of the existence of such forma- 
tions; yet there is sufficient evidence to cast doubt on the supposed 
twin-character of certain other double crystals of that mineral; and 
he further remarks that the statement of Weiss, to the effect that 
Quartz is but rarely disposed to form twin-crystals, has received 
confirmation on all sides. 
‘Kin Beitrag zur Kenntniss des Versteinerungs-Zustandes der 
