320 GEOLOGY OF THE CORDILLERA. [cHap. xv. 
masses are covered in the central parts, by a great thickness 
of red sandstone, conglomerate, and calcareous clay-slate, asso- 
ciated with, and passing into,-prodigions beds of gypsum. 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, crystallized 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° towards the Peu- 
quenes 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. Hence we must conclude, that 
both the Peuquenes and Portillo ranges were partially upheaved 
and exposed to wear and tear, when the conglomerate was form- 
ing; but as the beds of the conglomerate have been thrown off 
at an angle of 45° by the red Portillo granite (with the under- 
lying sandstone baked by it), we may feel sure, that the greater 
part of the injection and upheaval of the already partially 
formed Portillo line, took place after the accumulation of the 
conglomerate, and long after, the elevation of the Peuquenes 
ridge. So that the Portillo, the loftiest line in this part of the 
Cordillera, is not so old as the less lofty line of the Peuquenes. 
Evidence derived from an inclined stream of lava at the eastern 
base of the Portillo, might be adduced to show, that it owes part 
of its great height to elevations of a still later date. Looking 
to its earliest origin, the red granite seems to have been injected 
on an ancient pre-existing line of white granite and mica-slate. 
In most parts, perhaps in all parts, of the Cordillera, it may be 
concluded that each line has been formed by repeated upheavals 
