58o M. AU ROUSSEAU AND HENRY S. WASHINGTON 



Chemically the rock is a foyaite and differs in no essential 

 manner from the nephelite syenite. Indeed, the similarity of the 

 analyses of the nephelite syenite and of the nephelite porphyry is re- 

 markably striking. The latter contains less alumina and titanium 

 than the former, but is a very close parallel to it otherwise. What has 

 been said, therefore, of the affinities of the nephelite syenite applies 

 likewise to the nephehte porphyry. The specimen analyzed was 

 selected with care, and comes from the neighborhood of the peach 

 orchard mentioned. It is, as nearly as possible, the average 

 porphyry. 



The rock was analyzed independently by each of us. As the 

 summation from Washington's figures was low, and inspection 

 showed that the figures for alumina were probably at fault, the 

 average of the two analyses was taken, excluding the alumina from 

 I, and correcting that of II only by the deduction from it of one-half 

 of the difference between the two determinations of TiOj. Column 

 III represents the accepted values. On comparing the rock with ' 

 others of a similar nature, it is seen that it resembles the nephelite 

 porphyries of other localities. In particular may be mentioned the 

 nephelite porphyry of Julianehaab^ (Fox Bay t5T>e), wlii.ch is very 

 different mineralogically, however, and the nephelite syenite 

 porphyry of the Val dei Coccoletti, in the Tyrol.^ The last-named 

 rock is practically the chemical equivalent of the tinguaite of 

 Monte Mulatto, Predazzo, and indeed, so great is the chemical 

 resemblance of the Beemerville nephelite porphyry to certain 

 tinguaitic and leucitic rocks, that we quote the tinguaite of Monte 

 Mulatto (IV of Table II) in preference to the nephelite porphyry. 

 Column V is the nephelite porphyry of Umptek, a more sodic 

 rock, but otherwise similar; while VI and VII are respectively the 

 tinguaite of Hooper's Inlet, Dunedin, New Zealand, and a leucitite 

 from Kamerun. The similarity in chemical composition between 

 the Beemerville magma and the magma which has produced the richly 

 leucitic leucite phonolite of Poggio Muratella, Lake Bracciano, has 

 already been pointed out elsewhere.^ We desire to stress the simi- 



^N. V. Ussing, Geol. Julianekaab, Meddel. om Gronld., XXXVIII (1911), p. 275. 



2 J. Romberg, Sitzh., Preuss. Akad. Wiss., I (1911), p. 748. 



3H. S. Washington, The Roman Comagmatic Region (1906), p. 47. 



