GAWILGERII RANGE OF HILLS. 189 



1st. The principal part of the whole range is formed of compact 

 basalt, very much resembling that of the Giant's Causeway. It is found 

 columnar in many places, and at Gawilgerh, it appears stratified — the 

 summits of several ravines presenting a continued stratum of many thou- 

 sand yards in length. 



2dly. The basalt frequently and suddenly changes into a wacken, of 

 all degrees of induration, and, I may say, of every variety of composition 

 usually found among trap-rock ; 



3dly. Into a rock which may be named indifferently, nodular-wacken 

 or nodular-basalt, composed of nuclei of basalt, usually of great spe- 

 cific gravity, surrounded by concentric layers of a loose earthy mass, 

 resembling wacken, but without cohesion, which, on a superficial view, 

 conveys to the mind the idea of a fluid mass of earth, having, in 

 its descent from some higher spot, involved in its course all the 

 rounded masses it encountered, and, subsequently, become consolidated 

 by drying. A very slight inspection is sufficient to detect the true 

 cause of this appearance, which is owing to the facilities of decomposi- 

 tion of the outer crust, depending on difference of structure and compo- 

 sition. In none of the conglomerates, or pudding stones, do we observe 

 any traces of this structure, and as it is common to the most crystalline 

 green-stone, porphyritic green-stone, and those rocks usually denomi- 

 nated syenite, there can be little doubt that it is owing to the developement 

 of a peculiar concretionary structure by decomposition. In a small ravine, 

 near the village of Sdlminda, two thousand feet above the sea, I saw 

 basalt of a perfectly columnar structure, closely connected with a co- 

 lumnar mass formed of concentric lamellae, enclosing a heavy and hard 

 nucleus. Near this ravine, I had also an opportunity of observing the 

 gradual and perfect passage of the columnar basalt into that which has 



A 3 been 



