Dec. 186 i.] Geoloyy of the Xtihjherries, 237 



I have said that the Basalt appears in the bank of a horse-shoe 

 hollow, in a ridge branching from Snowdon. These hollows are 

 very common along the sides of the hills. They are distinct fiom 

 the ravines, the origin of which is due to the degrading operation 

 of running water, as well as from land slips, and I am disposed to 

 consider them as excavations wrought by the action of eddies in 

 those torrents that scooped out the contiguous vallies. 



In the neighbourhood of these hollows, traversmg a mass of 

 Syenite, is a Pegmatite consisting of large chrystals of Felspar 

 concreted, and traversed with plates of Prase Quartz. Between 

 the Chrystals of Felspar very delicate dendritic stains of oxide of 

 manganese occur. 



In taking leave of the subject of the Schist, to describe which 

 has been the paramount object of this portion of the paper, I have 

 to add that transported pieces of it occur in the valley to the West 

 of Snowdon, associated with numerous blocks of common syenite, 

 green syenite, and garnet rock. 



A variety of metalloidal diallage occurs in this locality : this 

 mineral has a silky shining lustre in one direction, is of a reddish 

 brown color, sometimes greenish and like bronze, and has a 

 lamellar structure with indications of a prismatic primary form. 

 Under the Blow Pipe, per se, it loses its color, becoming black 

 and more compact: with borax fuses into a green glass bead. 

 Streak grey ; yields easily to the knife ; contains a small proportion 

 of oxide of iron. Resembles, in some respect or other, Hypers- 

 tbene (Labrador Hornblende) Schillerspar, and Bronzite, all 

 Diallages. 



Returning from the heights above Snowdon to Ootacemund, one 

 is struck with a resemblance of the bason in which the Canton- 

 ment stands, to the crater of a volcano in a state of repose, but 

 this notion is entirely unsupported by facts, as there is nothing to 

 shew that one ever existed, 



Having accomplished my survey of Snowdon, the peak of which 

 is now almost always enveloped in a mantle of mist, I addressed 

 myself to investigate the character of the rocks of the amphitheatre 

 of which it forms one arm. 



