838 HENRY S. WASHINGTON 



the two. Its position is, however, not exactly intermediate, 

 since the large amount of magnesia and the presence of olivine 

 throw it somewhat out of line. For these effusive rocks, char- 

 acterized mineralogically by the presence of orthoclase with 

 basic plagioclase, augite or diopside, and olivine, and chemically 

 by rather low silica (53-58 per cent.), high magnesia and 

 potash, high alkalis, with more potash than soda, and ande- 

 sitic amounts of alumina, iron, and lime, I would propose the 

 name of ciminite,^ from their earliest known and most character- 

 istic locality. It may be mentioned here that these rocks, as 

 well as the vulsinites, show many analogies with the absarokite- 

 banakite series from the Yellowstone Park described by Iddings.^ 

 Their relations with these, as well as with the other trachy- 

 andesitic and the leucitic rocks of Italy will be discussed in the 

 final paper. 



'^Peperiiio." — With the above may be described a rock con- 

 cerning whose true character there has been much conflict of 

 opinion. This is a soft, incoherent rock, easily cut with tools, 

 which is much used for building purposes in the neighborhood. 

 It goes locally by the name of "peperino," and was called by 

 Brocchi "necrolite," on account of its use by the Etruscans for 

 their sarcophagi and for the excavation of their tomb-chambers. 

 It is quarried extensively at Bagnaia, to the east of Viterbo, 

 where it rests on Pliocene beds and forms the oldest known 

 product of the Ciminian eruptions. 



This rock is called by vom Rath a trachyte, by Verri a 

 trachytic tuff, by Mercalli a "quartz-bearing andesitic trachyte" 

 or dacite, and by Deecke a mica-andesite. There is thus here, 

 as in so many other instances, a great discrepancy among the 

 various writers in regard to its character. The rock is too 

 abundant, and too well known and much used in the region, and 

 the descriptions tally too well to allow us to entertain the idea 

 that the various observers are dealing with different materials. 

 In this case I must decidedly agree with Verri in calling it a 



• 3 Pronounced chiminite. 



= This Journal, III, 935, 1895. 



