ITALIAN PETROLOGICAL SKETCHES 847 



forming systems at right angles. These are best developed at 

 the borders of the crystal. Haiiyne is occasionally seen included 

 in, and hence older than, large orthoclase phenocrysts. 



The groundmass is holocrystalline and composed of small 

 asgirine prisms and alkali feldspar laths scattered through a paste 

 of nepheline, which occasionally shows characteristic crystal 

 boundaries. The powdered rock gelatinizes abundantly with 

 acids, the solution furnishing cubes of sodium chloride, and 

 staining of the slides renders the identity of the nepheline cer- 

 tain. There are also present some small magnetite grains, quite 

 abundant apatite needles, and a number of bright colorless 

 highl}- refracting grains and crystals of titanite, which often show 

 the characteristic p^yramidal forms and rhombic sections. No 

 leucite was seen. 



An analysis of this rock by the writer is given in Table II, 

 No. 9, the alkali percentages being the means of Na20 = 4.86 

 and 4.90, and K20 = 9.2i and 9.06, so that their relative amounts 

 are beyond question. The analysis by vom Rath of his "phono- 

 litic trachyte" is shown by No. 10. It would seem possible that 

 there has been a transposition of the figures for the alkalis in 

 vom Rath's paper.' This phonolite is then noteworthy for its 

 very high potash content, which explains the large amount of 

 orthoclase seen in thin sections. The amount of lime being very 

 small and having been exhausted in the formation of diopside, and 

 the potash having taken up most of the silica to form orthoclase 

 the soda left from the segirine went chiefly into nepheline rather 

 than into albite. 



Mercalli describes the above rocks under the name of " haiiy- 

 nitic sanidinite," but does not mention nepheline, though he 

 says that they have the megascopic characters of phonolite. The 

 description of the rock which vom Rath (p. 580) calls a phono- 

 lite-like trachyte from the Ciminian Mountains answers in every 

 way to those just described, except that it is said by him to con- 

 tain leucite and that it is quarried. The exact locality is not 



' The discrepancy between the analysis and the description of the rock is com- 

 mented on by ZiRKEL (Lehrbuch, II, 467;. 



