In these upper beds shells are tolerably frequent; and they belong to about the period of the lower chalk of Europe.

It is an old story, but not the less wonderful, to hear of shells which were once crawling on the bottom of the sea, now standing nearly 14,000 feet above its level.

The lower beds in this great pile of strata have been dislocated, baked, crystallised and almost blended together, through the agency of mountain masses of a peculiar white soda-granitic rock.
The other main line, namely, that of the Portillo, is of a totally different formation: it consists chiefly of grand bare pinnacles of a red potash-granite, which low down on the western flank are covered by a sandstone, converted by the former heat into a quartz-rock.

On the quartz there rest beds of a conglomerate several thousand feet in thickness, which have been upheaved by the red granite, and dip at an angle of 45 degrees towards the Peuquenes line.

I was astonished to find that this conglomerate was partly composed of pebbles, derived from the rocks, with their fossil shells, of the Peuquenes range; and partly of red potash-granite, like that of the Portillo.