812 THE GEOLOGY OP MINNESOTA. 



[Feldspar schist. Jaspilyte. 



the decay and disappearance of the older grains of the other feldspar. Fine sericite 

 scales also are abundant, but they are uniformly distributed, without forming any 

 schistosity. One section. 



Age. Archean (Upper Keewatin). 



Remark. With the exception of a little argillyte at the west end of this island, 

 the whole north shore of Ely island consists of rock of this kind. N. H. w. 



No. 1959. PELDSPAK SCHIST. ( Chloritic.} 



On the mainland southeast from Ely island. 

 Ref. Annual Report, xxii, page 1C. 



Meg. Fine grained, slightly greenish. At the "contact" or transition to 

 jaspilyte. 



Mic. This rock differs from No. 1957 in having better-preserved old feldspar* 

 (though still replaced by the same micro-granulitic alteration) and a notable amount 

 of a green isotropic substance which is the same as frequently appears in the green- 

 wackes, and also large grains of quartz. One section. 



Age. Archean (Keewatin). N. H. w. 



No. 1960. JASPILYTE. 



North side of the North ridge at Soudan. 

 Ref. Annual Report, xxii, page 16. 



Meg. Showing a distribution of iron ore in such a manner as to give the 

 appearance of squeezed pebbles of different colors. 



Mic. While the rock consists essentially of interlocking quartz grains in the 

 well-known manner of jaspilyte, it is colored by magnetite in such a manner as to 

 bring out more or less roundish outlines. Where the iron ore is abundant, or even 

 present in any amount, the fineness of the quartz grains is greater. One section. 



Age. Archean (Lower Keewatin). 



Remark. The variation in the size of the quartz grains where the iron ore 

 appears, indicates that the ore was present in some form at the date of formation of 

 the quartz, and has not been infiltrated since, and hence that it is not the result of 

 later concentration. N> H> w _ 



No. 1961. JASPILYTE. 



Same place as the last. 



Ref. Annual Report, xxii, page 16. 



Meg. Apparently pebbles, pressed, enclosed in hematitic jaspilyte. 



Mic. The pebble-like appearance is due, as in the last, to the peculiar manner 

 of distribution of iron ore in the siliceous mass. This slide, being more abundantly 

 supplied with iron ore, does not exhibit the same variation in the fineness of the quartz 

 grains. It shows, however, that the iron was present even before the micro-granu- 



