285 



forming one side of an acute rhombic pyramid ; these faces are all perfect, {. e., 

 smooth and brilliant, giving perfect reflections of light in any part ; the other 

 is a form very common in barytes, viz., pinacoid macrodoma, and brachydoma. 

 This group was attached by the bottle-shaped mass of amorphous sulphur. 



No. 5 is similar in structure to No. 4, but rather more complicated. 



No. 6 is a series of pyramids attached by their apices, and having branches 

 growing out of their sides. 



No. 7 is a curious bent pyramid, but has nothing very interesting about it. 



The groups 4 and 5 are not mere geniculations, as might be thought at first 

 sight, for the direction of the new foim is determined not by an asis, but by 

 the theoretical direction of the face requived to close the first or original form ; 

 again the faces are perfect, and not built up of alternate prisms and pyramids. 



Nos. 1, 3, and 6, may be regarded as common macles, inasmuch as the 

 axes are coincident. 



I also detected a few oblique rhombic prisms, which would indicate that 

 the crystals had been formed at a high temperature, or in the presence of 

 steam. 



Art. LI. — On the Nomenclature of Rocks. By E. H. Davis, F.C.S., F.G.S., 

 of the Geological Survey Department. 



[Read before the Wellington PldlosopMcal Society, Sejyfember 17, 1S70.] 



The nomenclature of rocks is a subject which is involved in considerable 

 confusion, and I regret to observe that geologists, instead of working 

 together and helping to clear it up, are doing their best to make the con- 

 fusion more confounded, by each one foUowicg a diSerent system as far as 

 possible, and thus not only making scientific intercourse difficult, but giving 

 rise to no end of quibbles about words ; — also, inducing a very loose way of 

 thinking, and rendering all induction impossible. This lamentable state of things 

 is more particularly striking in tbe case of syenites, and the purpose of this 

 paper is to call attention to the difference between the English and American 

 schools, as represented by Lyell, Dana, and Jukes, and the German schools, as 

 represented by Bischof, "Werner, Cotta, etc. ; — the latter using the term syenite 

 to express a distinctly plutonic basic rock, poor in magnesia, and closely allied 

 to diorite and its congeners ; the former using it to express an acidic rock, rich 

 in magnesia, and allied to granite, gneiss, and schist ; thus the one points to 

 the probable presence of tin, copper, lead, and zinc, while the other only points 

 to antimony and zinc. Gold and silver are common to both. 



Tn all cases this difference is highly objectionable, but especially so here in 

 New Zealand, where so little is known of the true structure of the country, 

 and many parts are seldom visited by white men, it is of .the highest 

 importance that every one should call the same thing by the same name. 



