354 ME. A. M. EINIAYSON ON THE NEPHRITE [Aug. 1909, 



Description of Special Areas. 

 (1) Parapara. 



This occurrence, which has been described by Dr. Bell [9, p. 66], 

 consists of a group of talc-serpentine rocks cropping out in the gorge 

 of the Parapara River, 7 miles south of Collingwood township. 

 The rocks are generally much foliated, indicating a high degree of 

 dynamic metamorphism, and contain a good deal of magnesite and 

 grains of chromite. The serpentine occasionally contains residual 

 grains of olivine, but is more usually of the laminated type, showing 

 under the microscope a fairly typical antigorite-structure. There is 

 no evidence as to the particular mineral from which the antigorite 

 has been derived, and it appears to be essentially the result of great 

 pressure. 



Effects of contact-metamorphism caused by the intrusion consist 

 in the development of corundum crystals, and more notably of tour- 

 maline in the surrounding schists [9, p. 67]. The tourmaline 

 crystals are of varying size, the average length being half an inch ; 

 but occasionally they are very coarse, measuring as much as an 

 inch in width and 8 or more inches in length. The smaller crystals 

 occur grouped in roughly radial fashion ; while the larger show a 

 remarkable cross-fracture, repeated along their length, and imparting 

 to the crystals often a stepped appearance. The effect is evidently 

 a result of considerable pressure on the less resistant rock which 

 contains them. The colour of the crystals is dark green to black,, 

 and the following analysis indicates an iron-magnesia variety : — 



Si0 2 36-80 



B,0 - 3 1041 



Al.A 25-37 



Fe"0 3 013 



FeO 6-12 



CaO 231 



MgO 12-91 



Na,0 1-20 



K,0 045 



Li o trace 



H 2 3-95 



E" trace 



Total 99-65 



Under the microscope (PI. XV, fig. 1), the tourmaline-bearing 

 rock is seen to be composed of coarse elongated crystals of tourmaline 

 and bunches of granular magnetite in a matrix of foliated chlorite 

 with some serpentine. The chlorite folia are distorted in passing- 

 round the included crystals of tourmaline and magnetite, im- 

 parting to the rock an ' augen-structure.' The pleochroism of the 

 tourmaline crystals is pink to bluish-grey, with strong absorption. 

 Good octagonal cross-sections are sometimes seen, which show a 

 corroded and altered centre, with separation of secondary magnetite. 



