NOD ULA R-BEA RING SCHIS TS 



495 



this interesting effect. It is to be noticed that, in general, the 

 thicker portions are on the same phase of the fold. 



The occurrence of the greatest interest lies in the second area 

 mentioned above. This is a belt of schist about one hundred 

 feet wide, full of ellipsoidal nodules which vary in length from 

 one to four inches along the greatest axis. As they are harder 

 than the schist, they weather out in relief, and immediately sug- 

 gest to the beholder the "prune granite" of Quincy, Mass., 

 excepting that the "prunes" are in this case lighter in color than 



Fig. 2. — lolite schist, showing projecting nodules. 



the rock mass. The accompanying photograph of specimens of 

 the rock will afford an idea of their appearance (Fig. 2). 



Upon microscopic examination these nodules prove of unusual 

 interest, because they largely consist of, or have been derived 

 from, a mineral which has had very little notice in North Ameri- 

 can petrography, namely, iolite. Except as an accessory in 

 certain basic rocks in Minnesota and as a mineralogical occur- 

 rence in various localities in the East, it has scarcely been men- 

 tioned. Abroad, however, it has frequently been described.' 



Only surface material was available for study, and in this the 



iolite, as is usually the case, is much altered, the common altera- 



^Vzde Zeit.fiir Kryst., Vol. XXIX, p. 305 ; also Vol. XXXI, p. 248 ; Neiies Jahr- 

 buch,No\. XI (1899), p. 84 ; Bull, de la Soc. de Sc. Boitcarest, Roumanie, Vol. III. 



