359 



stituents include several varieties of pyroxene, hornblende and biotite. 

 The typical rocks of the group are thoroughly granitic in texture, but 

 there are transitional forms which connect the elseolite-syenites with 

 the phonolites. Miascite, foyaite and ditroite are merely varieties of 

 elseolite-syenite. The group is exceptionally rich in accessory minerals. 

 Minerals containing the rare elements, thorium, yttrium, cerium, lan- 

 thanum, didymium, niobium, &c., occur in veins in these rocks. 



Foyaite. Term applied by BLUM to a rock occurring in the mountains 

 of Monchique in Southern Portugal. This rock was defined by him 

 as a crystalline granular compound of orthoclase, elseolite and horn- 

 blende. WERVEKE^) has shown that the dominant ferro-magnesian 

 mineral is augite and not hornblende. The latter mineral does, however, 

 occur. Some authors use the term foyaite as synonymous with elseolite- 

 syenite. 



Miascite. Term introduced by G. ROSE for a rock occurring in 

 the Dm en Mountains in Russia, essentially composed of orthoclase, elseolite 

 and dark mica. 



Ditroite. Term applied to a rock occurring at Ditro (Hungary), 

 essentially composed of orthoclase, elseolite, cancrinite and blue sodalite 

 (chlor-hauyn). Hornblende and segirine are present, but do not enter 

 largely into its composition. A characteristic feature of the typical 

 ditroite is the abundance of brilliant blue sodalite. Ditroite may, there- 

 fore, be described as a variety of elseolite-syenite exceptionally rich in 

 sodalite. 



Teschenite. This name was introduced by HOHENEGGER for certain 

 rocks which are intrusive in the Cretaceous strata of Silesia and Moravia. 

 The rocks in question were subdivided by TSCHERMAK into two groups 

 picrites and teschenites. The teschenite of TSCHERMAK^ is a crystalline 

 granular rock, composed of felspar, hornblende, augite and analcime ; 

 with magnetite, biotite, apatite, natrolite and apophyllite in smaller 

 quantities. ZIRKEL and ROSENBUSCH have both recorded the occurrence 

 of nepheline in this rock. TSCHERMAK described a rock from the 

 Caucasus under the name teschenite, and mentioned the existence of 

 nepheline in this rock. MACPHERSONW described a rock from Cezimbra 

 (Portugal) as teschenite, and also recorded the occurrence of nepheline. 

 According to ROHRBACH, however, all these authors have been mistaken 

 as to the existence of nepheline/ 5 ) so that at present it is doubtful 

 whether the teschenites should be classed with the nepheline-bearing 

 rocks or not. 



Tkeralite. This term has been proposed by ROSENBUSCH for plutonic 

 rocks characterized by the occurrence of plagioclase and nepheline. The 



(1) N.J., 1880, Band II., p. 141. 



(2) Die Porphyrgesteine Osterreichs. Wien, 1869, p. 258. 



(3) T.M.M., 1872, p. 107. 



(4) B.S.G.F., 3rd Se. T. X. (1882), p. 289. 



(5) T.M.M., Band VII., 1886, p. 29. 



