SYENITE OCCURRING IN PORTUGAL, AT 
Silica sacs tes Sieh anon 56°23 per cent. 
Sequioxide of iron ...... OA, 
Propoxide of ironly.. =... OPA. 
FAUNA hts iA tos seayiatic ye ZOO a 
IEATTTUS) AN, a ae AS Se ase PAR NS alae 
NM poTRO STA CS huts pets dates 0-40, 
SOG deerssseeiait< terst eis aya sice sic SOA oe 
GLASS Arp Neots steep sles BBB): Is 
Irena HOG! Ce Ries cows bok OPA 
IBhosploniclacids yb t. OPI ae. 
Suliphumic acidy jes aera. OO Onume 
COL Ios es 2) Seer meee Unsere ORC TO Wa 
iWishobinw whit. ous ica IOO 
99°34, 
Such is the mineralogical and chemical composition of Foyaite. 
It shows that in virtue of its essential constituents, coupled with 
the absence of quartz, this rock is a true eleolitic syenite belonging 
.to the more ancient eruptive series, accompanied by porphyritic 
varieties of the same, and by corresponding phonolitic varieties of 
Tertiary origin. By its wealth of rare but purely adventitious 
minerals it bears a close resemblance to ditroite (Transylvania), 
miascite (Siberia), and certain syenites of Brevig and Cape Verd, 
most of which are fully described in the luminous works of Prof. 
Zirkel, Vom Rath, Rosenbusch, and others. Hence there is no 
apparent reason why the nomenclature of petrology should be 
further encumbered by a special group of Foyaites, more especially as 
microscopic investigation of rocks is constantly producing fresh 
evidence not only of the infinite variety, but of the beautiful 
simplicity of Nature. 
EXPLANATION OF THE PLATES. 
Puate I, 
Fig. 1. Plan of Foya District, Portugal. Altitudes in metres. 
2. Section of ditto. 
Puare [I. 
Fig. 1. Section of Foyaite, showing nosean crystal surrounded by belt of soda- 
lite, with interpositions of magnetite and apatite, and associated with 
elxolite, augite, hornblende, biotite, titanite, &c. Magnified 20 dia- 
meters. 
2. Section of Foyaite, showing hornblende crystal with augite nucleus, with 
associated minerals, Magnified 20 diameters. 
