272 
Mr. Weaver on the 
position. These are in fact the successive outcrops of massy beds, 
composed of limestone and trap, in alternation with each other; 
and the south side of the valley is bordered by low hills and slight 
eminences, which partake of the same character. The country is 
thus constituted of seven or eight great alternating beds of lime- 
stone and trap, independently of the subordinate divisions that arise 
from the interposition of smaller beds of limestone in the latter ; as 
for example in Pallis hill. The general inclination of these massy 
beds is toward the west or south, at an angle of 10° or 12°. But 
the trap beds frequently possess in themselves an internal arrange- 
ment different from, and independent of the general disposition, 
(see also § 71.) 
§ 173. The trap rocks, which I have observed in this district, 
are iron claystone, greenstone, basaltic greenstone, all of them 
occasionally porphyrytic ; basalt, both amorphous and figurate; 
amygdaloid, felspar porphyry, and trap conglomerate. These rocks 
exhibit those endless varieties of aspect, which every where dis- 
tinguish them, but of which an adequate conception can scarcely 
be conveyed in words. I shall therefore attempt to describe only 
the prominent characters of the more distinct varieties. 
The basalt is greyish black, minute granular, displaying glim- 
mering facettes when exposed to the sun. It passes into basaltic 
greenstone of a blackish green, and this into compact greenstone of 
a greenish grey colour. These generally contain more or less of 
crystalline hornblende. The amygdaloid has commonly a base of 
decomposing greenstone, or of wacke, of a greenish grey or brown- 
ish red colour, enveloping nuts and points of calcareous spar. In 
the felspar porphyry, the base is usually light yellowish or reddish 
brown, or greenish grey, with a fracture passing from close granular 
to compact, sometimes approaching to the nature of clinkstone por- 
