6l2 



HENRY S. WASHINGTON 



Magnet Cove rocks that albite, as well as anorthite and horn- 

 blende, are of very limited occurrence. 



Covite {''Shonki?iite"^. — The specimen of this rock, which is 

 Williams's " fine grained syenite," came from below the school- 

 house on the western border of the Cove, and the analysis was 

 published in my former paper. It is repeated here, with the 

 addition of PgOg, which has been determined since. Several 

 analyses of analogous rocks are also given. 



I. Covite, Below Schoolhouse, Magnet Cove. Washington, analyst. Bull. Geol. 

 Soc. Amer., Vol. XI, p. 399, 1900. 

 II. Theralite, Gordon's Butte, Crazy Mountains, Montana. Hillebrand, analyst. 

 J. E. Wolff, Bull. No. 130 U. S. Geol. Surv., p. 201, 1898. 



III. " Tinguaite," Two Buttes, Colo. Hillebrand, analyst. Bull. 148 U. S. Geol. 

 Surv., p. 182, 1897. 



IV. Shonkinite, Yogo Peak, Little Belt Mountains, Montana. Hillebrand, analyst. 

 Weed and Pirsson, Am. Jour. Set., Vol. L, p. 474, 1895. 



V. Essexite, Salem Neck, Mass. Washington, analyst. JoUR. Geol., Vol. VII, 

 P- 57, 1899- 



The mineralogical composition of these rocks is such that 

 their calculation must, of necessity, be arbitrary and only 



