ITALIA N PE TR OL O GICA L SKE TCHES 3 6 1 



be augite-toscanites, while those of Monte Amiata would be 

 hyperstheiic-toscanite , if such a subdivision be deemed advisable. 



In Table III are given the best analyses of the representa- 

 tive Italian toscanites. Those from Bracciano, Cerveteri, and 

 Tolfa (Nos. I, 2, 3, 4, and 5) have been already described. 

 Attention need only be called to the richness of the San Vito 

 rock in NagO relative to KgO, as shown by Dr. Rohrig's analy- 

 sis, and confirmed by mine made later. In this respect it is 

 notable among the rocks analyzed by me. The rocks of Monte 

 Amiata, whose composition is given in No. 5, have been so fully 

 described by J. F. Williams, that the reader is referred to his 

 paper. ^ The rocks of Campiglia and Rocca Strada, Nos. 7, 8, 

 9, and 10, are purely biotite-toscanites and are all quartz-bear- 

 ing. It will be observed that the pyroxene-bearing toscanites 

 (1-6) are notably less acid than those which carry only biotite. 



Trachydolerites elsetvhere. — Having thus reviewed the main 

 feature of the trachydolerites along the Bolsena- Vesuvius line, 

 it will be of interest to see if such rocks are found elsewhere. 

 Their geographically nearest counterparts are found in the 

 Lipari Islands where vulsinites and ciminites occur according to 

 the descriptions of Sabatini^ and Mercalli.3 It must be noted, 

 however, that these are not very abundant and are associated 

 with true rhyolites, andesites, and basalts, and not with leucitic 

 rocks. Some of the rocks of Monte Ferru in Sardinia and of 

 the Ponza Islands may also belong to this group, though there 

 is doubt as to the character of the plagioclase, and they may be 

 rather trachyandesites. Another example of such transition 

 rocks is found at the Azores, where Hartung^ in i860 noted the 

 presence of rocks intermediate between the trachytes and the 

 basalts, which he called by Abich's name of trachydolerite. 

 The later investigations of Miigge^ have established the presence 

 of such rocks, though we are again left in doubt as to the char- 



'J. F. Williams, Neu. Jahrb. B. B., V, 403 ff., 1887. 

 = CoRTESEE Sabatini, Isole Eolie, Rome, 1892. 

 3MERCALLI, Giorn. Min., Ill, 97, 1892. 

 ■• Hartung, Die Azoren, Leipzig, i860, 291, 319. 

 sMiJGGE, Neu. Jahrb., 1883, II, 201. 



