The Uspallata range is separated from the main Cordillera by a long narrow plain or 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.