154 r. EUTLEY on BOTJTEILLEI^STEnf. 



patches showing distinct cleavage, and also in aggregates of smaller 

 elongated crystals apparently squeezed together with their longest 

 axis in the direction of the foliation. The felspars are triclinic, and 

 from the extinctions in some of the crj-stals, they appear to he 

 anorthite, the angles made hy the direction of maximum extinction 

 with the edge formed by the faces o P and oo Poo being 39° and 40°. 

 Other felspar crystals in the section give, however, very different 

 angles ; one, for instance, extingaishes at 18° from the datum-edge 

 in the + direction of Max Schuster, an angle which corresponds with 

 that of brachj-pinakoidal sections of albite ; but apart from the cases 

 of anorthite, the extinctions in these preparations are not very 

 trustworthy. A splinter of felspar taken from this specimen imparts, 

 however, a very strong yellow colour to the blow-pipe flame, so that 

 it is quite probable that albite is present. 



Note on the BouTEiLLEisrsTEDf, or Psetjdo-chetsolite, of 



MOLDATTTHEZN^ in BoHEMIA. 



BouteiUensteia occurs in small irregularly shaped nodules and 

 grains in sand near Moldauthein in Bohemia, in tuffs in the 

 neighbourhood of Mont Dore les Bains, and Pessy, in the Auvergnei, 

 and in one or two other localities. These nodules have peculiarly 

 pitted, corrugated, or wrinked surfaces, which I think are due 

 to irregular glass enclosures and gas-pores, which, on the sur- 

 faces of the nodules, have been broken through and partially 

 worn away. The glass of which these nodules consist is considered 

 by Zirkel, Eosenbusch, Von Lasaulx, and others, to be one of 

 the purest glasses occurring in nature. A section of a small bouteil- 

 lenstein nodule, leut me by Prof. Judd, shows a considerable 

 number of gas-pores and glass enclosures, and is traversed from one 

 end to the other by distinct and approximately parallel banding, 

 such as may be seen in many osbidians, but especially in a red one 

 from the Yellowstone district, figured in vol. xxxvii. of the 

 Quarterly Journal of this Society (pi. xx. fig. 2). In describing 

 this specimen I noted that some of the bands showed very distinct 

 depolarization between crossed nicols, and that extinction occurred 

 when the bands were brought parallel to the principal section of 

 one of the nicols. The bands in the bonteillenstein behave in a 

 precisely similar manner, and in both cases the phenomenon may be 

 attributed to strain*. The section contains numerous spherical gas- 

 bubbles and irregular glass enclosures, some fusiform, others club- 

 shaped, while many assume curious bulbous and slightly branching 

 forms. They are frequently produced into, or from, delicate capil- 

 lary rods, and they usually contain several, sometimes a dozen or 

 more, spherical gas-bubbles. The surfaces of these glass enclosures 

 do not, as a rule, appear to be smooth and cylindrical, but they 



* Observations upon depolarization in connexion with strain are best made 

 by artificial illumination, and the observer should screen aU extraneous 

 light from the eye. This may be done by wrapping a handkerchief round the 

 eye-piece. 



