44 HENRY S. WASHINGTON 



Brazil/ and Montana.^ It is difificult to understand why the 

 small groundmass leucites should suffer this change, while the 

 larger phenocrysts remain preeminently fresh and unaltered. 



Bucca does not describe any of the leucite rocks of the 

 Bracciano region. 



THE CERVETERI REGION. 



This region 3 lies about lo''™ southwest of Lake Bracciano 

 and north of the small town of Cerveteri, so famous for its 

 Etruscan tombs. It consists of a small group of hills, extend- 

 ing about 8^" W. N. W. and E. S. E. (about parallel with the 

 coast line, and 4 to 5'^'" broad. They are of no very great alti- 

 tude, the hills reaching their maximum height of 384 meters in 

 Monte Cerchiara, in the center of the group. I could only spend 

 the better part of one day at the eastern end, but as far as my 

 observations permitted me to judge they are a mass of domal 

 eruptions resting, as Tittoni points out, on Pliocene beds. 



They are composed almost exclusively of acid non-leucitic 

 rocks and their tuffs. Some leucitite is met with at the eastern end, 

 but these leucitic lava streams probably belong to the Bracciano 

 volcano proper. Since this leucitite is met with beneath the 

 "trachytic" masses, its occurrence is of great interest as showing 

 that the earliest leucitic outflows of Bracciano are of an earlier 

 date than those of Cerveteri, though they continued after these 

 latter had ceased. There seems to me to be an intimate con- 

 nection between the Bracciano center and that of Cerveteri, and 

 probably also that of Tolfa, but my opportunities for observation 

 were so few that I do not feel able to discuss this point at 

 present. 



Toscanite. — To this group belong all the specimens collected 

 by myself, and also apparently all those described by Bucca, 

 except those of a few leucitites. Their prominent mineralogical 

 and chemical characteristics have already been noted. 



' HussAK, Neu. Jahrb. 1892, II, 146. 



^ PiRSSON, Am. Jour. Sci., II, 194, 1896. 



3 It is included on the Bracciano Sheet (Foglio 143) of the Italian Geologic Map. 



