TUN 
2 56 Essay, &e. 
character of this stone on the surface as well as 
in the fracture; but ic differs from the others 
hitherto observed on the present route, in evi- 
dently remaining on the spot where it was form- 
ed, being. on the whole, connected to one mass, 
not rounded on the surface, or exhibiting blunt 
angles, as those referred to in the preceding des-: 
cription, both such as Ves ad in the beds 
of rivers, or dispersed among Basaltic rocks 
through the hills It appears, in my opinion, 
to come near to that species of lava which is 
distinguished very properly by Sir G. Mackenzie 
(sec Travels in Iceland) by the name of Ca- 
vernous lava: I soon met it again in investigat- 
ing che Southern coast, and it afterwards occur- 
red, both in exposed situations, where it is acted 
on by the Ocean and in the midst of the central 
ny 
ic has appeared of importance to point out 
those minerals which remain in their original 
situation, and define the extent of the volcanic 
chasm in the bowels of the earth, as in most 
parts of the Island, although consisting almost 
exclusively of volcanic materials, these have 
been removed from the place where. they were 
probably, Vic t 3 great distance from the spot 
where they were acted upon the  subterrane- 
ous cause. The constitution of the entire series 
of the irregular central ranges, is a proof of 
this, and after this mineralogical sketch of the 
route, I shall endeavour to point out (with re- 
ference to the map) these points which remain 
in their original state, and those See have 
been arranged in strata. 
