MUSEUM OF COMPARATIVE ZOOLOGY. 165 



(sericite) in the usual interwoven aggregates, irregular plates of chlo- 

 rite, grains of quartz, occasional crystals of albite and the ottrelite, in 

 small irregular plates with the usual pleochroism, etc., which sometimes 

 appear spindle-shaped in cross-section (discoid). Small, irregular black 

 metallic plates also occur in the rock. 



The Taconic region of Greylock Mountain, the highest summit in 

 Massachusetts, lies immediately west of the Hoosac series, extending 

 west in turn to the Taconic range, which forms the boundary between 

 New York and Massachusetts. The rocks of this area are in large 

 part phyllites of many varieties and colors, often dotted with crystals 

 of albite like the similar rock of Hoosac Mountain, containing garnets, 

 tourmaline, etc. The black metallic plates are wide-spread in these 

 phyllites, exhibit the same properties, such as very feeble magnetism, 

 diiUcult solubility in hydrochloric acid, presence of titanium, etc., that 

 those from the Ehode Island graphite schists do ; they are therefore 

 ilmenite. 



In the slides these rocks are composed of sericite, generally intimately 

 interwoven with chlorite, and small grains of quartz. Masses of black 

 ore, prisms of rutile, etc., are abundant. In some varieties the albitic 

 feldspar becomes an essential constituent. Tlie ilmenite plates are 

 commonly sandwiched between two plates of dark green chlorite, exactly 

 as in the Rhode Island rocks. In many of these rocks microscopic 

 plates of ottrelite, spindle-shaped in cross-section, exist enclosed in the 

 meshes of the mica. 



April, 1890. 



