1829.] 
found in the Gdivilgerh Range of Hills. 
357 
cultivating small patches of land, which produce a coarse rice and millet. In for- 
mer years, the cultivation must have been very extensive, since there are the ruins 
of numerous hill-forts and villages, which derived their chief subsistence from 
the surrounding lands. 
Many opportunities are affordedof studying the nature of this mountainousrange 
in tlie numerous ravines, torrents, and precipitous descents, which abound in every 
part. A Wernerian would not hesitate in pronouncing them to be of the “ newest 
floetz-trap formation,” aHuttonian would call them “ overlying rocks,” and a mo- 
dern geologist would pronounce, that they owed their origin to sub-marine vol- 
canoes. 
I shall not give them any other name, than the general one of trap-rocks ; but 
proceed to describe them, and state with diffidence the inferences which, I think, 
obviously present themselves on an attentive study of their phenomena. 
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 Gdwilgerli, it appears stratified ; the summits of several ravines pre- 
senting a continued stratum of many thousand 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 maylie named, indifferently, nodular-wacken or nodu- 
lar-basalt, composed of nuclei of basalt, usually of great specific gravity, surround- 
ed 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 ap- 
pearance, which is owing to the facilities of decomposition of the outer crust, de- 
pending on difference of structure and composition. In none of the conglomerates, 
or pudding stones, do we observe auy traces of this structure, and as it is common 
to the most crystalline green-stone, porphyritic green-stone, and those rocks 
usually denominated syenite, there can be little doubt, that it is owing to the de- 
velopement of a peculiar concretionary structure by decomposition. In a small 
ravine, near the village of Salminda, two thousand feet above the sea, I saw basalt 
of a perfectly columnar structure, closely connected with a columnar mass formed 
of concentric lamella’, inclosing a heavy and hard nucleus. Near this ravine, I bad 
also an opportunity of observing the gradual and perfect passage of the columnar 
basalt into that which lias been called stratified, from the parallelism of its planes ; 
the composition being identical, and, without doubt, cotemporaneons. These changes 
and passages, from one rock into the other, are so frequent and various, as to 
render it impossible to refer the most of them to either of the rocks I have 
above mentioned as types. I shall, therefore, proceed to describe those which 
are distinctly marked, and their accompanying minerals. In external appearance, 
(he columnar and semi-colunmarhasaltclosely resembles that of theGaint’s Cause- 
way, possessing the same fracture, internal dark colour, and external brown 
crust. It is equally compact and sonorous. It, however, contains more fre- 
quently, crystals of olivine, of basaltic hornblende, and of carbonate of lime. 
The fusibility of each is the same. Perhaps the basalt of the GSwilgerh range 
more nearly resembles in every respect, that of the Pouce mountain in the 
Mauritius. This is, however, of very little importance, since every body, who has 
travelled much in trap countries, knows well what great changes in composition and 
structure occur, even in continuous masses. Among the minerals, calcedony, and the 
different species of zeolite, are rarely found in the columnar basalt, but" they are 
of frequent occurrence iu that which is semi-columnar. 
The waken, or indurated clay, is as various in character and composition as the 
basalt, and unfortunately, I have no type with which to compare it, as in the case 
of the basalt of the Giant’s Causeway. Its colour varies with its constituents, 
but is most usually gray. It is easily frangible, very frequently friable, and is 
almost always porous and ainygdaloidal. It appears to be composed of earthy 
felspar and hornblende, with a considerable proportion of oxyd of iron. It is 
always easily fusible into a black scoria or glass, according to the quantity of 
zeolite which it contains ; of all the trap-rocks, it abounds the most in simple 
minerals. 
They are — Quartz. 
Calcedony and calcedonic agates, enclosing crystals of carbonate of lime. 
Common and Semi-opal. 
