94 B. KOTO. 



and there a brown diallage (2-4 cm.) is sporadically distributed. 



The rock has precisely the same structure possessed by the 

 "schillerspath" or "bastite" of the Harz Mountains, and fjllowing the 

 suggestion given by Geo. H. Williams,* the writer here uses the term 

 "poicilitic" for that structure. The diallage is provided with that 

 peculiar, finely striated appearance, which is well-known to be the 

 result of pressure.f In a large number of cases crystals are bent, 

 thereby presenting an appearance as in the case of mici-lamella?. 



The outlines of the diallage are very irregular, being traversed 

 by various cracks in all possible directions; consequently the original 

 crystallographic form is nowhere visible. 



The process of ' glaucophanization ' seems to have commenced 

 from the above-mentioned fissures and peripheries of individuals, 

 precisely in the same manner as that of olivine in becoming a 

 serpentine. One portion of crystals is, however, resolved into some- 

 what larger columnar individuals of glaucophane which have the same 

 optical orientation as the moth er- mineral. Transformation proceeds 

 molecule after molecule in so gradual a manner, that when the section 

 of diallage is at i. with the shorter diagonal of the polarizer, both the 

 glaucophane, and the original mineral are of a light brown, and we 

 can scarcely discern the boundary of the two. If the section is at 

 right angles to the former position, then the difference of colour 

 becomes at once quite distinct, one being a lavender-blue, the other a 

 brown. (Fig. I.) 



The glaucophane thus produced resolves itself again into the 

 glaucophane-asbestus which in turn, passes into a confused aggregate 

 of jninute fibres, assuming at the same time a grass-green colour. 



Prof. Bonny;]: has ably described a gabbro from Pegli near 



* Araeri. Journ. of Science, vol. xxxi, January, 1886, p. 30. 



t Vide. 0. Miigge, Neues Jabrbucli für Miu. etc., 1883, I., p. 84. 



I Geological Magazine, vol. VI., 1879, p. 363. 'Liugurian aud Tuscauiau Serpentine.' 



