582 CHILL 
One variety (properly amygdaloidal) contained small globules (or 
globular nodules) of quartz, thickly disseminated; and the globules 
were covered with a dark-green coating of chlorite or green earth. 
In this valley, loose boulders, apparently from the same rock, had a 
brownish-red tint, and were porphyritic with tables of feldspar about 
half an inch long and half a line thick. 
The non-porphyritic graystone, above alluded to, when in worn peb- 
bles, might be taken for an argillaceous rock ; but by its transitions to 
a variety having a porphyritic character, its true nature was apparent. 
On the ascent of the Andes near Santiago, the ejected rocks re- 
sembled many of the varieties described. Above, they became coarsely 
cellular in some places, and resembled a true lava, and red and purple 
shades of colour were common. The examinations were too hasty 
for minute descriptions. 
The high ridge back of Santiago, which appears to have been one 
of the centres of eruption along the line of the Andes, is a sublime ob- 
ject in the Chilian Cordilleras, and especially when seen from neigh- 
bouring heights among the mountains. When about eleven thousand 
feet above the level of the sea, a deep valley lay between us and its 
declivities. For six thousand feet, there was one long ashy slope ; so 
unvaried that even the sight of it seemed to produce the weariness of 
an ascent. Above, black rocks broke through a mantle of snow, in 
rude columns, some forming divergent groups, and others rising into 
turrets and crests. 
Direction of the Dikes.—The dikes vary much in direction, even in 
the same ridge, and without a thorough study of the whole country, it 
is difficult to deduce any conclusions of interest. 
One of the dikes, a league north of Valparaiso, trends southeast or 
south-southeast, and dips 50° to the northeastward. ‘The other has the 
same course, with a dip of sixty degrees. ‘These dikes are bounded 
on each side by a layer, a fourth to a third of an inch thick, consisting 
of a whitish argillaceous earth, which peels off readily. It is soft and 
crumbling, and resembles kaolin, and is probably the result of the 
friction against the granite walls produced by the injected greenstone 
as it ascended. 
In the Mellaca Hill, the dikes run generally to the northwestward. 
In the “third cuesta,” near San Felipe, where the dikes are 
numerous, the course is almost uniformly southeast, varying occasion- 
ally to east-by-south. At one place there were six dikes, from eight 
inches to six feet wide, in a distance of twenty feet. The intervening 
