CHILL 583 
walls of granite were narrower than the dikes, varying in width from 
six inches to three feet. ‘These dikes did not appear to have produced 
any alteration in the adjoining rock. 
In the Jaguel Valley, a dike of graystone cuts through a red por- 
phyroid sedimentary rock, and is changed nearly to a black colour 
adjoining the walls, while the red rock itself is deepened in tint. 
STRATIFIED OR SEDIMENTARY ROCKS. 
On the ascent of twelve thousand feet near Santiago, it appeared 
that the vast mass of the Andes consisted mainly of a conglomerate or 
earthy rock, having in many places the aspect of a porphyry, yet 
showing its composite character on a worn surface. The shades of 
colour were various, as red, yellow, gray, green, brown, purple, and 
several were sometimes in combination. The colour often varies 
at short distances, and occasionally a red colour or some other shade 
pervades a large part of a bluff vertically through several layers, 
without much lateral extent, or any appearance of its being con- 
nected with the stratification. The rock also appears to pass through 
very dark shades nearly to black. 
The structure of the rock varies from a coarse conglomerate, com- 
posed of rounded pebbles, twelve to fifteen inches in diameter, to a fine 
argillaceous deposit, more or less schistose; and between these ex- 
tremes, there is every possible variety. The pebbles of the conglome- 
rate are imbedded in a base which appeared to be argillaceous ; in some 
kinds the pebbles are closely compacted together, and in others they 
are scattered through this base. In the latter case, it is often difficult 
to distinguish the rock from a true porphyry, especially as the base 
often contains disseminated crystals of feldspar, and the pebbles may 
not be apparent on a surface of fresh fracture. A rock of this kind is 
used at times for a flagging-stone in Santiago, and unless carefully 
inspected, it would be set down at once as a red porphyry. 
The pebbles are as various in composition as the rocks of the moun- 
tains, consisting of different kinds of porphyry, porphyritic green- 
stone, graystone, trachyte; besides, there are others which have an 
argillaceous appearance: these may be portions of the above-mentioned 
rocks half decomposed. 
The rock sometimes assumes a hard compact structure and fine 
granular texture; and again it is soft and tufaceous in aspect. Some 
