1806.] Petrography. 395 



ellipsoidal or ovoid masses of feldspar and a little quartz, separated 

 from each other by narrow anastomosing partitions of green interstitial 

 substance composed of pyroxene and feldspar. When the ellipsoid* are 

 flattened by foliation the rock becomes a streaked gneiss. Under the 

 microscope, in sections of the coarse grained gneisses, large crystals of 

 pyroxene, microcline and quaitz are seen to be imbedded in a fine 

 grained aggregate of microcline and quartz. In the ellipsoidal varie- 

 ties the ellipsoids are composed mainly of microcline grains and the 

 interstitial mass is a fine grained mosaic of feldspar, quartz and augite. 

 In the streaked gneiss the augite is partially changed to green horn- 

 blende, while crystalloids of idiomorphic hornblende indicates that some 

 of this component is an original crystallization. The rocks are 

 evidently sheared pyroxene-syenites. The author discusses the use of 

 the term « gneiss ' and suggests that the term ' gneissoid ' be restricted 

 to the description of foliated eruptive rocks whose structure is due to 

 magma motions, that ' gneiss ' be used as a suffix to the name of any 

 rock that has assumed the typical gneissic structure since its original 

 consolidation, as diorite gneiss, etc., and that the ending ' ic ' be used 

 with reference to the mineralogic composition of a foliated rock whose 

 origin is unknown — a dioritic gneiss, in this sense indicates a folaited 

 rock whose present composition is that of a diorite. 



Petrographical Notes.— In thin sections of sandstone inclusions 

 that have been melted by basalts, Einne 7 finds the remains of quartz 

 grains surrounded by rims of monoclinic augite, cordierite, spinel, etc. 

 In some of the glasses formed by the melting of the sandstone are tri- 

 chites and crystallites of orthorhombic pyroxene. While this substance 

 is found abundantly as a contact mineral in the sandstones enclosed in 

 the basalts of Sababurg, the Blauen Kuppe and Steinberg, the author 

 nevertheless regards it as a comparatively rare product of the contact 

 action between these two rocks. 



Bauer 8 declares that the rubies, sapphires, spinels and other gem 

 minerals from northern Burma occur in a metamorphosed limestone on 

 its contact with an eruptive rock whose nature is not known. 



Penfield 9 obtains a heavy solution for the separation of mineral pow- 

 ders whose densities range between 4.6 and 4.94 by melting together 

 silver and thallium nitrates in different proportions. The molten mass 



d. Ges. z. Befdrd der geaamnet Naturw. Marburg, 1896, No. 

 . Journ. Sci., Dec-, 1895, p. 446. 



