PETRO GRAPH Y . 125 
cially ferrous, lime, and potash. That the last is very much too low is clear from 
the fact that 1.73 per cent of potash would furnish but 7.85 per cent of leucite, 
a figure which is only about one-quarter of the amount of this mineral actually 
present. The norm of analysis II would place the rock in auvergnose (with 
gabbros, diabases, and feldspar-basalts), no leucitic types of which have ever been 
described or probably could exist, and, furthermore, all rocks with high (about 
50 per cent) feldspar, especially plagioclase, which is almost wanting in the Monte 
Jugo rock, as we have seen. This analysis of Ricciardi's must then be rejected, 
as well as many others of similar rocks published in the above-cited paper by 
Klein, study of the norms and the possible mineral compositions showing them to 
be quite unreliable. 
Mode. The mode was calculated from the norm, the figures being checked so 
far as possible by study of sections under the microscope. In this calculation all the 
potash was assumed to go into leucite and the augite to have the usual composition. 
Labradorite, Ab 2 An 3 10.5 
Leucite 32 . 3 
Nephelite 3.4 
Augite 47.1 
Olivine 4.0 
Magnetite i . i 
Apatite i . o 
100.0 
Occurrence. This type is confined, apparently, to the Vulsinian District, the 
type specimen coming from the small parasitic cone of Monte Jugo, in the south- 
eastern part. Other specimens which may be referred here are from the quarry of 
Le Grazie near Montefiascone, from La Canonica near Orvieto, and from blocks 
southwest of Valentino. 
Name. The name of the subrang III. 7. 2. 2 is, of course, derived from that 
of the small cone from which comes the type specimen. The type rock from this 
locality is called by Klein* "a leucite-tephrite, passing into leucitite." In view of 
the very subordinate amount of feldspar it would seem that the name leucitite 
would be appropriate in prevailing classifications. 
QALERAL ALBANOSE-JUdOSE. II. 8-7. 2. 2. 
Megascopic characters. Very dark gray or black, compact, aphyric, or with very rare 
phenocrysts of leucite and augite. Groundmass aphanitic. 
Microscopic characters. Holocrystalline, microporphyritic, somewhat clathrate fabric. 
Microphenocrysts : about 45 per cent, leucite, augite. Microgroundmass: about 55 per cent, 
augite, labradorite, olivine, nephelite, magnetite, apatite. 
Labradorite, Ab 2 An 3 . Groundmass: about 10 per cent, anhedral, as formless interstitial 
areas. 
Leucite. Microphenocrysts: about 30 per cent, o.io to 0.20 mm., anhedral, equant, 
circular sections, inclusions few. 
Nephelite. Groundmass: less than 5 per cent, anhedral, formless, interstitial areas, diffi- 
cult to detect. 
* Klein, Neu. Jahrb., B. B. VI, 1889, p. 2 o. 
