214 PROF. J. W. GREGORY ON THE [May IC;OO t 



lavas would be limited to the character that it is a lava with a glassy 

 base containing phenocrysts of anorthoclase ; and that statement 

 as a definition of pantellerite Eosenbusch has emphatically re- 

 pudiated. No doubt the kenytes and pantellerites are closely 

 related, but I do not feel justified, on the evidence at present avail- 

 able, in radically altering Eosenbusch's diagnosis. It seems there- 

 fore advisable to give to these East African lavas the new name of 

 kenyte, from the mountain where they reach their highest 

 development. 



The kenytes may be defined as liparitic representatives of 

 an olivine-bearing nepheline- syenite, consisting of anorthoclase- 

 phenocrysts, with or without some augite- and olivine-phenocrysts, 

 and a glassy or hyalopilitic groundmass, which varies in colour from 

 greyish-green to a deep sepia-brown. JEgyrine, if present, occurs 

 in small granules ; senigmatite and quartz are absent. 



The kenytes are most nearly allied to the pantellerites, but are 

 probably as a rule more basic. Taking the average of the five 

 analyses of pantellerites quoted by Prof. Lcewinson-Lessing, 1 and 

 the formulce which he has calculated from them, pantellerite agrees 

 more nearly with the chemical composition of dacites than with 

 that of nepheline-syenites : — 



EO. R 2 3 . Si0 2 . Acidity. 



Pantellerites 2*34 1-40 1148 3'54 



Dacites 223 174 1124 302 



Trachytes 2-52 196 1026 2-42 



Nepheline-syenites 2-69 231 925 1-91 



Prof. Zirkel 2 quotes an analysis of a dacite with a higher soda- 

 percentage than is recorded for any of the five analyses of pan- 

 tellerites. The rock is from Zovon, west of Teolo, in the Euganean 

 Hills : it is described by Zirkel as having a ' light-coloured ground- 

 mass, with many large oligoclases from 3 to 4 lines long, also biotite 

 and hornblende ; much magnetite ... a little quartz in small druses ; 

 specific gravity 2*593.' From the analysis it appears not improbable 

 that this Teolo rock should be included among the pantellerites, and 

 that the mineral determined as oligoclase is really anorthoclase : — 



Dacite. Pantellerite. 



Si0 2 Silica 67*98 68-33 



A1 2 3 Alumina 1305 1094 



FeO Ferrous Oxide 374 



Fe 2 3 Ferric Oxide 5'69 541 



CaO Lime 163 1'36 



MgO Magnesia 0*14 016 



K Potash 3-23 4'08 



Na 2 Soda 7'96 709 



But if this Teolo dacite be a pantellerite, the fact that it has 

 been included among the dacites illustrates the chemical similarity 

 of these rocks. 



1 • Stud, iiber die Eruptivgest.' Congres Geol. Internat. Compt. Rend. 

 sess. vii, St. Petersb. (1897) pp. 449, 451, 453. 



2 ' Lehrbuch d. Petrogr.' 2nd ed. vol. ii (1894) pp. 575, 582. 



