Ila. 



[Ila. 



IV( 



15* 



.... | 

 lo'l j" 



14 



IV- 



20-3 



26 



36- 



29'8 



19 



31' 



29-9 



21 



186 U.S. Washington — Solvsbi rgite and Tinguaite. 



amount of aegirine went into solution, the figures given in the 

 table may be regarded as closely approximating to the truth. 

 Sodalite is neglected in the calculation, as the CI determination 

 is thought to be much too high, and none was seen in the 

 sections. Ila and h are Brogger's calculations of the Iled- 

 riim tinguaite (op. cit. 115, 191). As far as pyroxene and 

 orthoclase go the two correspond very well, but in the Massa- 

 chusetts rock analcite largely replaces the albite and nepheline 

 present in the other. YVa is the calculated composition of the 

 Foia tinguaite (op. cit. 259). 



la. 



Aegirine 10*2 



Pyroxene 3*3 



Orthoclase 1 7*3 



Albite.. 20-9 



Nepheline 10*9 



Analcite 37-4 



Sodalite .. 18* 



Accessories.. 1* 4-8 



The occurrence of analcite in tinguaite is by no means new, 

 Rosenbusch having noted it in our rock, Ramsay and Hack- 

 mann* in that of Umptek (No. YI), and Wolff and Tarrf in 

 that of the Crazy Mountains (No. VII). In a section of the 

 Hot Springs Tinguaite No. V (kindly given me by Prof. 

 Pirsson) the groundmass is seen to be sprinkled with clear, 

 isotropic patches, which may be nepheline cut basally or else 

 analcite, the grain being too line to show cleavage. The prob- 

 abilities are that they are analcite, as the appearance of the 

 section is too fresh to admit our attributing much of the 5*14 

 per cent H 2 to decomposition. It is a common constituent 

 of the closely analogous phonolites of Cripple Creek described 

 by Cross.J The authors of the first two papers, together with 

 Rosenbusch, regard the analcite as pseudomorphous after leu- 

 cite or some other mineral. Cross regards it as primary, when 

 discussing his phonolites. The possibility of the primary char- 

 acter of analcite in certain rocks has been upheld by Lindgren§ 

 and IddingsJ and in a recent extremely suggestive paper 

 Pirsson T has conclusively shown that what has been thought 

 to be glassy base in the monchiquites is in reality analcite, and 

 has greatly strengthened the arguments in favor of the occur- 

 rence of primary analcite in other rocks. In the present case 



* Ramsay and Hackmarm, Feimia 11, No. 2, 157, 1894. 

 + TVolfE and Tarr, Bull. Mus. Comp. Zool., xvi, 230, 1893. 

 % Cross, 16 Ann. Rep. U. S G. S., Pt. II, 32, 36, 1895. 

 §W. Lindgren, Proc. Cal. Acad. Sci. (2), iii, July, 1890. 

 II Iddings, Jour. Geol., i, 638, L893. 

 ■[[Pirsson, Jour. Geol., iv, 679, 1896. 



