354 HENR V S. WA SHING TON 



Orthoclase, ------ 'h'^A 



Albite, - - - - - - -15.2 



Anorthite, ------ 22.8 



Olivine, - - - - - - - 10.2 



Diopside, ...... 3.7 



Magnetite, ...... ^.o 



Accessory, ------ 0.7 



1 00.0 



I have also included among the ciminites, both on mineral- 

 ogical and chemical grounds, the well-known "trachyte" of 

 L'Arso on Ischia. This has long been known as an instance of 

 the exceptional occurrence of olivine in trachyte, and has been 

 taken by Rosenbusch' as the type of one subgroup of his "ande- 

 sitic trachytes." Judging from an examination of a number of 

 sections from specimens collected on the spot, plagioclase is not 

 as abundant as in the Viterbo or Bolsena rocks. There are, 

 however, some phenocrysts with multiple twinning lamellae 

 whose extinctions show them to be labradorite, Ab^^ An^ or 

 more basic ; and a certain portion of the groundmass feldspar 

 laths are of a similar plagioclase. Olivine, while present in my 

 specimens, is not as abundant as at Viterbo, but a colorless diop- 

 side or augite is the prominent and abundant ferromagnesian 

 constituent.^ These observations agree with the analyses by 

 Doelter of the main flow (No. 7) and of the scoria of the crater 

 at Le Cremate (No. 8), which show less magnesia and lime 

 and more alkali than in the typical ciminites. 



Though we possess no reliable analysis of it, the so-called 

 "biotite-trachyte" of Monte Catini in Tuscany may perhaps be 

 regarded as closely related to the ciminites. Both orthoclase 

 and a (basic ?) plagioclase are present and some pilite pseudo- 

 morphs after olivine are noted by Rosenbusch,^ who also remarks 

 upon its lamprophyric character. The rock is very remarkable 

 for the abundance of olivine along with biotite. 



'RoSENBUSCH, Mikr. Phys., II, 773, 1896. 



= I could find no traces of the leucite mentioned by vom Rath. 



3R0SENBUSCH, Neu. Jahrb., 1880, 206, and Mikr. Phys., II, 764, 1896. 



