HENRY S. WASHINGTON 



given. He does not mention nepheline but speaks of a mineral 

 in the groundmass which "may be sanidine," and states that the 

 rock gelatinizes abundantly with HCl. The analysis (No. 9, 

 Table II) is hardly that of a leucite-phonolite, so that the rock 

 may be classed as a phonolite with accessory leucite. 



A phonolite of a somewhat different character is from a lava 

 stream in the steep inner wall of Monte Vico, north of Monte 

 Venere. This is a compact fine-grained gray rock, highly vesicu- 

 lar in structure, with a few small nepheline crystals visible on the 

 walls of the vesicles. Glassy twinned tabular sanidines are 

 abundant. Under the microscope it is seen to belong rather to 

 the trachytoid type of Rosenbusch. The orthoclase phenocrysts 

 are similar to those of the preceding specimens, but the rare 

 pyroxene phenocrysts are rather augite proper than segirine- 

 augite. No haiiyne is to be seen, but shreds of much altered 

 brown biotite are found here and there. The groundmass is 

 quite trachytic in character, the eegirine needles being less 

 abundant and alkali feldspar laths much more so than in the 

 other type, with marked flow structure. These, with considerable 

 magnetite and some very small titanite grains, lie in a holocrys- 

 talline paste of what is apparently a mixture of orthoclase and 

 nepheline. The former is in somewhat large flakes, and the 

 latter distinguishable by its very weak double refraction and its 

 behavior with acids. 



Deecke describes some true phonolites which form two 

 dikes in the eastern crater wall of Monte Vico. They correspond 

 very closely to those described above. It is worthy of note that 

 phonolite also occurs as a dike at Le Braidi on the eastern flank 

 of Monte Vulture, ^ij but has not been observed among the other 

 products of this volcano. 



A?ialyses. — In Table II are given the most reliable of the few 

 analyses of the rocks of this region. No. 5 was made for me 

 by Dr. A. Rohrig of Leipzig. No. 2 was made in the Mineral- 

 ogical-Petrographical Laboratory of Yale University under the 

 direction of Professor L. V. Pirsson, to whom I take the opportunity 



^Deecke, New Jahrb., B. Bd. VII, 602, 1891. 



