46 HENRY S. WASHINGTON 



firmed by my analysis given in Table I, No. 2, which may be 

 taken as representative of the rocks of this region. 



The rocks of Monte Lungo and Monte Ercole, west of Monte 

 Cucco, are rather darker and rougher in groundmass, and look like 

 the Arsotrachyte of Ischia, minus olivine. The plagioclase is, 

 however, rather more basic, having a composition Ab^An^, and 

 the biotite rather browner in tone though still green, and colorless 

 diopside phenocrysts rather more frequent. The glass base is 

 rather dark brown, and the small orthoclase keraunoids are much 

 more abundant, as are also the diopside microlites, which are here 

 prismatic in habit. The rock of Belvedere del Principe south 

 of Monte Ercole, is also closely similar in general characters, 

 but the orthoclase keraunoids are here so abundant as to give 

 the base a hyalopilitic structure. The glass is brown and the 

 diopside microlites are prismatic in habit and show some flow 

 structure. 



It may be noted that absolutely no magnetite is to be found 

 in any of these rocks. Small apatite needles are found in all, 

 especially as inclusions in the feldspars. Bucca mentions a 

 brown hornblende as present, known by its prismatic angle and 

 oblique extinction, but careful research failed to reveal it in my 

 specimens. As has been said, analysis No. 2 of the Monte 

 Cucco rock may be regarded as representative of them all, and 

 its close resemblance to that of the Tolfa and Calvario rocks will 

 be noted. Further remarks on these points must be reserved 

 for the final paper. 



Leucitite. — This is represented by a specimen from a flow 

 met with at the bottom, of the deep ravine immediately to the 

 west of Monte Cucco, whose rocks overlie it, though tuffs and 

 soil conceal the contact. It is almost identical with the leucitites 

 from the south of Lake Bracciano, and is composed essentially 

 of round and irregular leucites with insterstitial green augite 

 needles. Some magnetite and a very little orthoclase are also 

 present. 



The rock of which the ruined Castle Dannato is built was 

 obtained from some now forgotten quarry in the neighborhood. 



