174 



W. II. IIOP.BS — METAMORPIIISM OF BERKSHIRE SCHISTS. 



In one instance stains of iron oxide were observed to traverse the enlarge- 

 ment and stop abruptly at its junctions with the core (figure 3,5). 



Staurolite. — This mineral has only been found in the central schist bed. 

 It is usually macroscopic and its crystals sometimes attain to a length 

 of two or three centimeters. They are bounded by the usual forms, and 

 are frequently twinned in inclined crosses. The color is usually black, 

 but is sometimes cinnamon-brown. Under the microscope the mineral 

 presents the usual characters with strong pleochroism. like the garnet, 

 it is sometimes compact, sometimes very ragged, from inclosures of the 

 matrix. Secondary enlargements have not been determined, but the 

 observation of crystals with an outer zone which, unlike the center, is 

 free from inclusions, makes their occurrence not improbable. 



Figure 3.— Garnets with secondary Enlargements. 

 From schist of Johnny's mountain, near Sheffield. 



Reactionary Rims of Staurolite and Magnetite about Garnet. — The arrange- 

 ment of staurolite and garnet is in some instances such as to show that 

 the staurolite is a later development. Its crystals seem sometimes to be 

 developed about and near garnets, as in the rock from the Lion's Head, 

 northwest of Salisbury (number 3431). In the schists of the north end 

 of the ridge called June mountain (northeast of Sheffield village), a crown 

 of staurolite prisms almost encircles an individual of garnet (number 

 3306 B). The garnet is pink, and is filled with microlites (rutile). Be- 

 tween the encircling crown of roughly radial staurolite crystals and the 

 garnet individual is considerable magnetite (see figure 4). The fact that 

 staurolite has not been found except with garnet, though garnet is found 

 unaccompanied by staurolite, taken in connection with the statements 

 just made, shows that staurolite has generally been a later development 

 in the rock, and probably requires more intense metamorphism. In 

 some instances, at least, it is indebted to the garnet for its iron and 

 probably also much of its alumina and silica. In the ease of the crown 

 about garnet, we seem to have a true reactionary rim, where the iron of 



