Vol. 57.] MOUNT GIRXAE, JF^AGAEU. 41 



another ' analcite-basalfc ' from Colorado [22]. The rock contains, 

 besides augite, olivine, and magnetite, a 'considerable amount of 

 a colourless and isotropic substance both in large and small grains ' 

 without crj^stalline form. The groundmass consists of small grains 

 of the material in question and of augite, magnetite, and felspar. 

 Further, we are told that : 



'The larger grains are almost wholly free from inclusions. While probably 

 the last substance to crystallize, the isotropic mineral has pushed back the 

 smaller grains of augite and magnetite, so that they often form a distinct zone 

 about it.' ^ 



The fracture is irregular. Beeke's method showed its index of 

 refraction to be less than that of Canada balsam. It was sepa- 

 rated and analysed (see p. 47), and has approximatel}' the compo- 

 sition of analcime. The low proportion of silica in this analysis is 

 attributed to the probable presence of nepheline among the felspar. 

 An ' analcite-tingnaite ' from Essex County (Massachusetts) has 

 been described as follows by Mr. H. S. Washington [23] : 



* The clear colourless micro -groundmass .... is holocrystalline, and com- 

 posed of nepheline and analcite .... The patches of analcite are readily dis- 

 tinguished by their cubic cleavage, exhibited by well-defined straighte cracks 

 crossing at right angles, by their generally isotropic character, and by the fact 

 that their refractive index is notably lower than that of the felspars. In 

 places they show a very faint double-refraction analogous to that of leucite, 

 but not so well marked. . . . The analcite areas are rather poorer [in inclusions] 

 than those of nepheline.' 



This rock is said not to be associated with nepheline-rocks, and 

 Mr. Washington does not believe that it differs appreciably in 

 chemical composition from an ordinary basalt, except by the presence 

 of water. 



The three rocks last referred to ought not, I think, to be included 

 among the monchiquites, as in them the isotropic material does not 

 form the groundmass of the rock. It seems clear that it is in 

 each case a primary constituent. 



III. A Rock with a Monchiquite-Matrix, from Mount 

 GiRNAR. (See PI. II.) 



I now proceed to give a brief description of a rock which presents 

 many points of resemblance to the m on chi quite-type. In the year 

 1893 and the earlier months of 18134, 1 was engaged in a geological 

 survey of the State of Junagarh in Kathiawar, and soon recognized 

 the occurrence of ne})heline-syenite in the small isolated mountain- 



* While no crystalline form was observed, rings or wreaths of small inclu- 

 sions were noticed in a. few grains, and these so strongly suggested leucite that, 

 until the chemical analysis had been completed, he thought that the rock was 

 a leucite-bisalt. Occasionally the grains have a smoky tinge, and in a few 

 cases the colouring-matter is arranged in zones clearly suggesting a crystalline 

 form. Leucite also has been found (in missourite) in 'formless masses filling the 

 interspaces between other minerals.' It is ' perfectly clear and free from all 

 inclusions, except now and then a grain of tlie ferromagnesian minerals.' [SO] 



