GRANITIC AND ALLIED ROCKS. 563 
in structure, and approaches an argillaceous shale, though less slaty ; 
it appears to contain a little hornblende. A few rods north, there are 
similar intercalations of a gneissoid rock having the same dip, which 
are black with hornblende, though presenting a fine texture like the 
micaceous rock just referred to. The lines in the figures show the 
direction of lamination. 
The hornblende, in some places, forms small disseminated concre- 
tions half an inch in diameter, scattered through the granite, and there 
are also a few isolated ovoidal masses, 
as in figure 3, representing twelve feet. 
The granite still contains mica; but a 
short distance farther to the north, it 
begins to be hornblendic, through a 
gradual replacement of the mica by 
this mineral. The hornblende at first 
is rather soft, and of a green colour, and could scarcely be distin- 
guished from chlorite except by the more decided hornblendic cha- 
racter exhibited a little farther to the north, where the rock is a true 
syenite. The pseudo-dikes of compact hornblendic schist, now be- 
come more extensive and appear like thick layers: they constitute a 
considerable portion of the coast. 
Both the granite and the hornblende schist are frequently inter- 
sected by the same feldspathic veins, and they often contain magnetic 
iron ore. In some instances, however, a feldspathic vein is faulted 
by the syenitic schist, as shown in figure 1. 
The dark globular spots which have been referred to as occurring 
in these rocks, include generally a larger proportion of mica or horn- 
blende than occurs in the parts around. They rarely exhibit a con- 
centric structure. In one instance, the inclosing rock was concentric, 
though the ovoid mass itself was tough and compact. 
Just north of Valparaiso, on the shores, there are small concretions 
in the granite, two or three inches in diameter, which consist of a 
feldspar exterior about half an inch thick, with a dark micaceous 
centre containing small deep-red garnets. No garnets occur in the 
adjoining rock. ‘The nodules are scattered quite thickly through the 
rock, and look somewhat like imbedded fossils. Over the water-worn 
surface of the rocks many of these concretions are partly worn off, and 
only half the feldspathic shell remains, emptied by abrasion of its 
micaceous material and garnets. 
On the way beyond Vina del Mar towards the Concon the rock is 
generally a granite; but at several places there are transitions similar 
