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VOLCANIC ROCKS 105 
parts of this mountain. If this author may be correctly understood, 
rocks with name of „lamprophyres“ are partly younger crosscut- 
ting dikes, partly great inclusions in the batholith and thence elder 
than the granite. The latter types are probably identical with the 
above described amphibolite inclusions. There are seen but little 
of real crosscutting dikes of lamprophyres in this mountain, as far 
as I know.! The relations of these to the above described quartz 
porphyry (keratophyric) dikes have not been made clear by obser- 
vations. — 
In the ,abyssal“ part of the Cerro Cordobés there has been disco- 
vered a great number of lamprophyric dikes, independently cutting 
across the old rock members. In these dikes the rock is always dense 
and of black greenish colour. There appears a jointing, causing 
a partition into angular blocks. Microscopically it reveals a porphy- 
ritic structure composed of small phenocrysts of plagioclase and 
a groundmass of granular amphibole of green colour, intermingled 
with small feldspar grains. The plagioclase phenocrysts are not 
more closely determinable, because they are intensely altered. The 
-_ amphibole has the ordinary habit. A parallel orientation of minerals 
in the rocks structure lacks completely, also every sign of pressure. 
_ The groundmass is more of a hornfels nature. It seems quite pro- 
bable, that the rock belongs to the malchitic type (Rosenbusch). 
It is remarkable, that the amphibole is more abundant than the 
plagioclase and thence also more abundant than in the ordinary 
amphibolite. | 
There is in the limestone banks, occurring as concordant bands 
in the profiles of the Quebrada Cordobes (eastern slope of the 
Sierra de Umango ridge), a crosscutting lamprophyric dike, having 
in handspecimen a dense habit. By microscope one can see, that 
the structure is an ophitic one. The mafic mineral is an elongated 
augite, oriented in like divergent directions as the plagioclase laths. 
1 From the collections of Bodenbender. 
