

F. L. Bansome — Lava Flows of California. 369 



the table of chemical analyses. Concerning this rock Wash- 

 ington writes : " Vom Rath first called attention to the abnormal 

 chemical character of the ' trachyte ' of Bolsena, though he 

 speaks of it as containing no plagioclase, probably owing to 

 the rarity of the multiple twinning. As will be seen from 

 Klein's descriptions and my own, and from the analyses, the 

 peculiar 'trachytes' of the region are remarkable: mineralogi- 

 cally for their richness in plagioclase and the frequent occur- 

 rence of olivine as an essential constituent,. and chemically for 

 their low silica and high lime and magnesia. Therefore they 

 are not trachytes proper, but correspond to the trachy-dolerites 

 of Abich and Hartung, and to some of the andesitic-trachytes 

 of Rosenbusch, and we shall see that they may be regarded as 

 effusive representatives of Brogger's abyssal monzonites. 

 These olivine free effusive rocks will be called by the name of 

 Vulsinite from the Etruscan tribe Yulsinii, formerly inhabit- 

 ing this region."* There is thus fresh confirmation of the 

 result already stated, that the latites of the present paper 

 belong neither with the normal trachytes nor yet with the 

 normal andesites, but occupy a position chemically about 

 midway between the two. 



Effusive rocks with a chemical composition corresponding to 

 this intermediate taxonomic position appear to be not uncom- 

 mon, and on pages 365 and 366, the chemical analyses of a num- 

 ber of such rocks have been placed together in tabular form. 

 Numbers I to XIX inclusive are analyses of latites, which in 

 the table are given the names assigned them by the authors 

 quoted. Numbers XX and XXI, in the middle division 

 of the table, are a typical andesite and typical trachyte respec- 

 tively, being inserted to show the intermediate character of the 

 latites. The latter as a whole form a fairly uniform chemical 

 series. 



But when attention is directed to the names and descriptions 

 of the various effusive rocks embraced in the table, they are 

 found to be remarkable more for variety than uniformity. 

 Thus, besides the latites described in the present paper, 

 there occur such names as ciminite, biotite-vulsinite, olivine- 

 bearing andesitic trachyte, vulsinite, andesite, angite-andesite, 

 trachyte, biotite-dacite, and sanidine-bearing andesite. At first 

 glance such an abundance of names for effusive rocks of a 

 single chemical type seems to indicate little else than a state of 

 hopeless confusion in rock nomenclature. But while a certain 

 amount of confusion does undoubtedly exist, the multiplicity 

 of names has its chief explanation suggested by two other 

 facts — partly, as pointed out by Iddings,f that rock-series as 



* Italian Petrological Sketches, Journal of Geology, vol. iv, p. 547. 

 f Journal of Geology, vol. iii, pp. 955-95G. 



