412 E. S. BASTIN 



abundant minute crystals of hematite, the latter frequently grouped 

 in aggregates; this in turn passes into a vesicular, dark gray mass in 

 which distinct quartz fragments are absent, the iron largely in the 

 form of magnetite, and cordierite very extensively developed; some 

 feldspar may perhaps be present, but could not be identified. 



The complete crystallization of a vein of slag one-tenth of an inch 

 across, and the perfect development of many of the crystals, are 

 probably to be explained by high temperature of the rock walls when 

 the slag flowed in, and a consequent slow cooling. In general, the 

 physical conditions under which the metamorphism took place are 

 similar to those in the slag furnace, and the resulting products are 

 slaglike in appearance. The materials involved are, however, some- 

 what different from those of most slags. They are typical pelites, 

 and it is not surprising that one of the minerals most abundantly 

 developed, cordierite, should be a mineral rarely found in artificial 

 slags, but one of the commonest minerals developed in the contact 

 metamorphism of pelitic sediments. 



