Joly — On the Penological Examination of Road-metal. 349 



amounts to about one-fifth of the rock. There is a little magnetite 

 or ilmenite present. The texture is a little finer than X; the 

 structure not quite so ophitic. 



XIII. Geological formation, d 1 G n B. 



Like X. in appearance, but a little coarser in grain. It is 

 tough under hammer, giving a rough fracture. After five years' 

 wear is much rounded and smoothed on surfaces. 



Microscope. — A coarser grain than X. Felspars fresh and in 

 places ophitic towards an abundant augite. The latter much altered 

 to serpentine, and in every case veined with this alteration-product. 

 A good deal of ilmenite or magnetite. (See fig. 2, Plate XXXII.) 



XIY. Geological formation, d 1 G n B. 



Like X. in colour, but coarser. The coarsest in texture so far 

 examined. Tough under hammer, and very rough in fracture. 

 After six years' wear not very much rounded, and surfaces still 

 rough. 



Microscope. — Practically same as XIII. Varying amount of 

 alteration- products in augite ; but in no case is this free from veins 

 of serpentine, etc. 



XV. Geological formation, Po c i- 



A fairly coarse dolerite, but finer in grain than the last. 

 Very tough, and giving a rough surface of fracture ; after ten 

 years' wear is fairly rounded. Practically the same as XIII. 

 and XIV. Augite as before, much decomposed ; and felspar fresh 

 and ophitic towards the augite. The latter is sometimes granular, 

 and then encroaches on the felspar. 



XVI. Geological formation, d 1 " B." 



A very rough, black dolerite, possessing, however, basaltic 

 characters. The coarsest in grain of the entire series. Under 

 hammer, very tough and rough. After five years' wear is 

 fairly round, but surface shows some of its original roughness. 



Microscope. — A very coarse rock with large fresh felspars some- 

 times ophitic in an augite considerably altered. Along with these, 

 large grains of olivine more or less serpentinized. A variolitic glass 

 often extends in radiating fibres from angles of felspar crystals. 

 There are a few well-shaped prismatic forms filled with alteration- 

 products of spherulitic appearance. Magnetite in large irregular 



