File:The Quarterly journal of the Geological Society of London (13889826060).jpg

252
J. H. COLLIJS'S ON THE GEOLOGY
often have fimbriated extremities as shown in fig. 1, where a is the
lode-fissure, 6 the porphyry, and c the slate.
Fig. 1. — Section showing Forpliyritic Masses.
a. Lode-fissure.
h. Porphyry,
Slate.
Their general direction is so similar to the strike of the slates, and
their length is so much greater than their breadth, that they appear
to be interstratified, unless the junctions are very closely examined.
"When, however, such, examinations are made, the true nature of the
association of the rocks is obvious enough, for the slates abut
against the porphyries without in any way bending round them, or
else the porphyry breaks up into branches and fingers, which,
are thrust between the laminae of the slates as in fig 1. This latter
mode of occurrence may be well seen on the hill above Puerto Eubio.
A bending of the laminas of slate around the porphyry is almost
if. not quite unknown.
In a few places the porphyrj^ appears to be much like granulite.
This is particularly observable between the Fuente Fria water-
deposit and the first llalaiio. Where the porphyries meet the slates
by a faulted junction, as is frequently the case, a thick mass of
" fault rock " is often observable at these junctions. This may be
verj^ well seen in the railway- cutting on the west side of the Mesa
de los Pinos (see fig. 2) and on the Zalamea road about half a mile
Fig. 2. — Section in Railway -cutting on the luest side of the Mesa
de los Pinos.
h. Porphyry.
Slafce.
d. Fault-rock.
west of Bella Yista, both localities being situated oii prolongations
of the " Yalley lode "*". It is also well seen at the foot of the hill

• In this railway -fault the slates (c) are inclined at a very high angle to the
  

north. They only appear to have a low angle because of the direction of the