354 
USPALL AT A PASS 
CHAP. 
basin, like those so often mentioned in Chile, but higher, being 
six thousand feet above the sea. This range has nearly the 
same geographical position with respect to the Cordillera, 
which the gigantic Portillo line has, but it is of a totally 
different origin : it consists of various kinds of submarine lava, 
alternating with volcanic sandstones and other remarkable 
sedimentary deposits ; the whole having a very close resemblance 
to some of the tertiary beds on the shores of the Pacific. From 
this resemblance I expected to find silicified wood, which is 
generally characteristic of those formations. I was gratified in 
a very extraordinary manner. In the central part of the range, 
at an elevation of about seven thousand feet, I observed on a 
bare slope some snow-white projecting columns. These were 
petrified trees, eleven being silicified, and from thirty to forty 
converted into coarsely-crystallised white calcareous spar. 
They were abruptly broken off, the upright stumps projecting 
a few feet above the ground. The trunks measured from three 
to five feet each in circumference. They stood a little way 
apart from each other, but the whole formed one group. Mr. 
Robert Brown has been kind enough to examine the wood: he 
says it belongs to the fir tribe, partaking of the character of the 
Araucarian family, but with some curious points of affinity 
with the yew. The volcanic sandstone in which the trees were 
embedded, and from the lower part of which they must have 
sprung, had accumulated in successive thin layers around their 
trunks ; and the stone yet retained the impression of the bark. 
It required little geological practice to interpret the marvel¬ 
lous story which this scene at once unfolded ; though I confess 
I was at first so much astonished that I could scarcely believe 
the plainest evidence. I saw the spot where a cluster of fine 
trees once waved their branches on the shores of the Atlantic, 
when that ocean (now driven back 700 miles) came to the foot 
of the Andes. I saw that they had sprung from a volcanic 
soil which had been raised above the level of the sea, and that 
subsequently this dry land, with its upright trees, had been let 
down into the depths of the ocean. In these depths, the 
formerly dry land was covered by sedimentary beds, and these 
again by enormous streams of submarine lava—one such mass 
attaining the thickness of a thousand feet; and these deluges 
of molten stone and aqueous deposits five times alternately had 
