GRANITIC AND ALLIED ROCKS. 561 
tures of the landscape. This is the case with the bottom of the nar- 
rower valleys, excepting those among the Cordilleras; and the wide 
plains are but the bottoms of wider valleys. The hills about the 
plains of Santiago appear like islands in a quiet sea; for the slopes do 
not decline into the plain by a gradual blending, but terminate ab- 
ruptly below, as if the country had been levelled off around the stand- 
ing eminences. ‘The same is true of the plains of Aconcagua, and of 
the valley of the Concon through all its extent. The rivers, in conse- 
quence of the level character of the valleys, usually run in three or 
four shallow pebbly channels, which are united by cross courses, 
forming together a network of water over the valley-plain. In the 
thawing season, these shallow fordable streams become deep and dan- 
gerous torrents. ‘They often rise rapidly; and as the melting in the 
mountains ceases at night, there is a periodical rise and fall of water 
in the course of the day. 
There appears to be no want of fertility in any part of Chili, except 
such as results from a lack of water. ‘This is the principal obstacle 
to cultivation, and it is extensively overcome by artificial irrigation. 
Over the dreariest waste, a line of rich green is observed wherever 
there is a trickling streamlet to afford the needed moisture. 
GRANITIC SERIES OF ROCKS. 
Granitic rocks, with which we include gneiss, syenite, and mica 
and hornblende schist, constitute the coast of Chili in the vicinity 
of Valparaiso, as well as to the north and south, and occur here 
and there over the country to the Andes. Extensive exploration 
would be required to make a map showing accurately their distri- 
bution, since they occur among the trachytic, porphyritic, and green- 
stone ridges, instead of being separated in a range of country by 
themselves. Between Quillota and San Felipe, the first cuesta, four 
miles from the former city, and about nine leagues from the sea, con- 
sists of trachyte; the second, twenty miles beyond, is composed of 
porphyritic greenstone; the ¢herd, twelve miles farther to the north- 
east, 1s granitic, with numerous greenstone dikes; at Quillota, Mel- 
laca Hill is granite. It is hence impossible to draw a direct line 
between the coast and the Andes, dividing all the granitic from other 
igneous rocks. 
The granite of the coast near Valparaiso is, to a great extent, gneis- 
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