So much for the western line; in the Portillo pass, proceeding eastward, we meet an immense mass of conglomerate, dipping to the west 45 deg, which rest on micaceous sandstone, etc., etc., upheaved and converted into quartz-rock penetrated by dykes from the very grand mass of protogine (large crystals of quartz, red feldspar, and occasional little chlorite).

Now this conglomerate which reposes on and dips from the protogene 45 deg consists of the peculiar rocks of the first described chain, pebbles of the black rock with shells, green sandstone, etc., etc.

It is hence manifest that the upheaval (and deposition at least of part) of the grand eastern chain is entirely posterior to the western.

To the north in the Uspallata pass, we have also a fact of the same class.

Bear this in mind: it will help to make you believe what follows.