664 HENRY S. WASHINGTON 



than the core of syenite, which, though basic, is distinctly 

 leucocratic. The composition of the whole, then, would be 

 melanocratic, as demanded by the theory, though with notable 

 amounts of alkalis and alumina. The same general relations 

 are assumed by analogy for the previously described Square 

 Butte laccolith, whose magma thus possessed a similar strongly 

 melanocratic character, i. e., with a basic " solvent" portion, as 

 was suggested.' 



In this connection attention may be called to two other 

 examples of differentiated masses in which the borders are more 

 acid than the center. One is the igneous area at Alno,^ which 

 is of special interest, since the rocks of this locality are very 

 much like those of Magnet Cove. Another example is that of 

 the Rieserferner massif in the Tyrol as described by Becke.^ 

 The central part of this is a typical tonalite, while the borders 

 are composed of what is called " Randgranit." Although, 

 unfortunately, no analyses are given, it is very evident from the 

 descriptions and from the separations by heavy solutions that 

 the border rock is decidedly higher in alkalis (especially 

 potash) and silica than the main central mass. 



Another region which offers close analogies in many ways 

 with that under discussion is that of Ice River, in British 

 Columbia, the rocks of which, collected by Dr. G. M. Dawson, 

 have been briefly noticed by A. E. Barlow. "^ As the specimens 

 were collected on a hasty trip, nothing is as yet known of their 

 mutual relations in the area, but they form an unbroken series 

 " from the most basic ijolite containing 36.988 per cent, of silica, 

 to ordinary nepheline and sodalite syenites containing 53.638 

 per cent, of silica." Through the kindness of Dr. Barlow I 

 have been able to examine sections of the ijolite, and it is inter- 

 esting to note that, while closely analogous to the ijolites of 



' H. S. Washington, op. cit., p. 411. 



^HoGBOM, Afh. Sver. Geol. Unders., No. 148, 1S95. Map II. This is explained 

 by Hogbom as due to melting and absorption of the surrounding gneiss. 

 3F. Becke, Min. Pet. Mitlh., Vol. XIII, p. 379, 1893. 

 ■* A. E. Barlow, Science, N. S., Vol. XI, p. 1022, 1900. 



