144 
THE GEOLOGIST. 
port in the south-west portion of the island, and hurrying forward 
inland, in an easterly direction, towards the Geysirs. Passing through 
a variety of scenery, they come out at length to a wide plateau of 
lava,* stretching away for miles, barren and dismal, innumerable 
boulders — relics of the glacial period— encumbering their path. At 
length, at a distance of about five-and- thirty miles from Reykjavik, " I 
was arrested (says his lordship) in full career by a tremendous preci- 
pice, or rather chasm, which suddenly gaped beneath my feet, and com- 
pletely separated the barren plateau we had been so painfully traversing, 
from a lovely, gay, sunlit flat, ten miles broad, that lay — sunk at a 
lower level by a hundred feet — between us and the opposite mountains. 
I was never so completely taken by surprise. Sigurdr's purposely 
vague description of our halting-place was accounted for. 
" We had reached the famous Almanna Gja. Like a black rampart 
in the distance, the corresponding chasm of the Hrafna Gja, cut across 
the lower slope of the distant hills, and between them now slept in 
beauty and sunshine the broad verdant plain of Thingvalla. 
" Ages ago — who shall say how long — some vast commotion shook 
the foundations of the island, and, bubbling up from sources far away 
amid inland hills, a fiery deluge must have rushed down between their 
ridges, until, escaping from the narrow gorges, it found space to spread 
itself into one broad sheet of molten stone over an entire district of 
country, reducing its varied surface to one vast blackened level. 
" One of two things then occurred — either the vitrified mass con- 
tracting as it cooled, the centre area of fifty square miles burst asunder 
at either side from the adjoining plateau, and, sinking down to its pre- 
sent level, left the two parallel Gjas, or chasms, which form its lateral 
boundaries, to mark the limits of the disruption ; or else, while the pith 
or marrow of the lava was still in a fluid state, its upper surface became 
solid, and formed a roof between which the molten stream flowed on 
to lower levels, leaving a vast cavern, into which the upper crust sub- 
sequently plumped down." 
His lordship next proceeds to a detailed description of the 
section, as follows : — 
Trachyte, i.e., lava in which felspar predominates. 
