2 6 2 Will ia m s — Contact-meta m orph ism n ea r PeekshiM. 



farther to the east, and described at length in a former paper.* 



Their origin in both cases is without doubt essentially the 

 same. 



Group 2. Certain of the included masses in the diorite 

 higher up the hill are composed mainly of quartz. Nos. 10, 

 30 and 31 represent this class. The quartz grains contain the 

 well-known black, hair-like needles in greater perfection than 

 any which have ever come under my notice. These are often 

 arranged zonally forming a matted net-work, as it were, around 

 the principal axis of the quartz crystal, while the interior and 

 periphery are quite free from them. Many other accessory min 

 erals were observed in these quartz inclusions. These vary 

 very much in their amount and relative proportions. Those 

 noticed were magnetite, pleonaste. zircon, apatite, sphene, gar- 

 net, tourmaline, muscovite, green mica, biotite. hornblende and 

 plagioclase. 



Group 3 of the inclusions in the diorite are principally made 

 up" of staurolite and a green mica, associated with a greater or 

 less amount of sillimanite. Representatives of this class are 

 found in sections Xos. 9 and 11 of the University collection, 

 and among those belonging to Professor Dana, those marked 

 EW, EVT 1 and Or. S. The staurolite and sillimanite possess 

 the same characteristics which have already been described in 

 connection with the altered mica schists. The bright green, 

 micaceous mineral is a member of the chlorite group, as is 

 shown by its chemical behavior: while an optical examination 

 serves to more specifically identify it as ripidolite or dinochJore. 

 In prismatic sections it shows a decided pleochroism : — 0= green, 

 E= light yellowish green; absorption 0> E. Both its refrac- 

 tive index and its double refraction are very weak. Basal 

 cleavage sections in converged polarized light show a positive 

 interference figure with a small optical angle. The monoclinic 

 character is apparent from the bisectrix not standing quite nor- 

 mal to the basal pinacoid. Cleavage flakes of a typical ripido- 

 lite specimen from Westchester, Pa., examined for comparison, 

 yielded exactly similar results. 



There is no doubt that this green mica has been derived 

 from a brown biotite. for many incompletely changed crystals 

 show a gradual transition from the one mineral to the other. 

 The specific gravity of the green mica (2 "9), which is excep- 

 tionally high for clinochlore, is probably due to the fact that it 

 is still associated with more or less biotite. Accessory minerals 

 observed in the thin sections of the inclusions belonging to 

 Group 3 are garnet, tourmaline, corundum, quartz, feldspar, 



*This Journal. Ill, xxxiii. p. 194, March, 3 887. 



