196 THE CKYSTAL FALLS IKON-BEARING DISTEICT. 



mica have developed in great abundance. Mica is well known as one of 

 tlie minerals produced in gi'anite contacts, and it evidently here owes its 

 abundance to the presence of the granite. 



At a considerable distance from the nearest intrusive outcrop (2 miles) 

 a mica-schist was observed which was characterized by numerous small 

 but prominent nodules that stood out upon its weathered surface. The 

 rook contains a considerable C[uantity of an apparently original chlorite 

 in large automorphic plates. The nodules were produced by large individ- 

 uals of staurolite. The staurolite has almost completely altered, remnants 

 only of the original individuals remaining. These remaining grains show 

 a very poor cleavage, and extinguish parallel to it. These include blebs of 

 quartz and particles of iron oxide. The}^ have the usual pleoclxroism for 

 staurolite, varying from golden yellow for c to yellowish white for a and h. 

 The alteration products in which the grains lie are fine scaly aggregates 

 of minute leaves of muscovite, with here and there larger plates of the 

 same mineral. A few grains of quartz and a small amount of iron oxide, 

 possibly partly original, are found in the mass. This observation of the 

 alteration of the staurolite to muscovite confirms the observations of Thiir- 

 ach^ and Pichler.- A similar staurolitiferous mica-schist, occurring in the 

 same locality, was described by C. E. Wright for the Wisconsin survey.^ 

 On these particular specimens the characteristic twins of staurolite may be 

 observed macroscopically as well as in thin section. Wright has also 

 described a garnetiferous mica-schist from this area of metamorphic schists.^ 

 Both of these schists contain prisms of bluish tourmaline in considerable 

 quantity. 



It appears highly probable that these staurolitiferous and garnetiferous 

 schists owe their origin to the intrusion of the igneous rocks, though no 

 well-marked contact zones could be outlined. 



The exomorphic contact effect of the granite is more noticeable where 

 a large body of the granite contains a sedimentary intrusion than elsewhere. 



The determination of the sedimentary origin of the fragments included 

 in the granite is based primarily ujjon the probability that in its passage 



1 Tliiirach, Grotb's Zeitschr., Vol. II, p. 423. 



- A. Pichler, Beitriige zur Miner.alogie Tirols, Neues Jahrb., 1871, p. 54. 



'Geology of the Meuomiuee irou regioD, by C. E. Wright: Geol. of AViscocsin, Vol. Ill, 1878, Part 

 8, p. 695. 



^Loc. cit., p. 695. 



