236 Geology of the Xtilyherries. [No* 12, new fanres, 



porphyries, and Lydian stone : some of these I collected and pre- 

 sent a list of : 



1. Jasper marked with red waves on a white ground, passing 

 into green and red. 



2. Lydian stone traversed by veins of variously coloured 

 Porphyry, from brown to grey, environing chrystals of Felspar, 

 Amygdaloidal aggregations of Felspar, and dark green quartz, 

 dusted with pulverulent chrystals of Augite. The base of the 

 Porphyry is an indurated clay, having a streaky, almost fibrous 

 structure, and occasionally an Agate figuring. 



3. Red Porphyry enveloping the same minerals hs the former 

 and travering quartzose blocks. 



4. Schist with iron inserted between its leaves (this occurs in 

 transported masses AVest of Snowdon). 



Quitting the Basalt I proceeded along the ridge, and found it 

 consisted chiefly of Syenite with protruding massses of garnet 

 rock along its Western side. I broke out of one of these pieces 

 a garnet an inch in diameter. 



From some of the Syenitic blocks in this locality, project ser- 

 rated ridges cf Quartz the crests of Quartz veins. They furnish 

 good indications of the original capacities of the blocks, the ingre- 

 dients of which have decomposed and disappeared, leaving the 

 Quartz standing out. Nearly at the bottom of the ridge, where it 

 meets the terre-plein of the valley, terminations of masses of 

 Syenite project through the side of the Hill. 



Piled on each other they form natural caverns. 



The declination of the lateral natural joints of these rocks (for 

 they are generally split into prismatic blocks) at an angle seldom 

 under 2b° from the horizontal line, is a remarkable feature in the 

 Geology of this valley, and the fact receives an accession of in- 

 terest when we find the interior slopes cf the eminences flanking 

 it conformable to this dip, and remember we have seen the Schist 

 and Traps preserving the same declination. The expression dip, 

 is perhaps inadmissable when speaking of un-stratified rocks, but 

 there is no other that so well describes the slanting direction of 

 rocks whose lateral lines of cleavage are not horizontal. 



