AUGITE-SYENITE AND GRANITELL. 113 
kinds. In some kinds blackish and greenish-black points dot the rock 
rather sparsely, while occasionally a greenish substance is coarse enough to 
be recognizable as softened hornblende or augite. With diminishing coarse- 
ness of grain, there comes to be present in these rocks more or less of a 
matrix whose crystalline structure is not macroscopically recognizable, when 
there appears to be a passage towards the uncrystalline felsites above de- 
scribed. An increasing amount of the softened greenish mineral, along with 
an increasing amount of striated feldspar, accompanies in other varieties 
what appears macroscopically to be a passage toward the orthoclase-gabbros 
of the preceding part of this chapter. 
Under the microscope, as to the naked eye, these rocks are always 
found to be chiefly made up of the feldspars. These feldspars include, in 
most cases, a triclinic kind as well as the predominating orthoclase. In a 
few sections no plagioclases were recognized, but this may have been simply 
on account of their great alteration. The polarization angles obtained, and 
the general appearance of these plagioclases prove them to be oligoclase, 
or low down in the labradorite range. The feldspars are always turbid, 
and commonly also highly charged with red iron oxide. In the larger 
number of sections the feldspar crystals are charged also with secondary 
quartz, which occurs either in rows of club-shaped or ‘‘graphic” particles, 
which often follow the cleavage directions of the crystals, or in very fine 
lines radiating in fan-shape from a central line. As in the secondary quartz 
of the above-described felsitic porphyries, so also here, large clusters of 
adjacent and apparently separate particles are found to polarize together. 
In this case, however, it is the particles belonging to one feldspar crystal 
which are thus similarly oriented. Particles and needles of brown and 
black ferrite are also often present in these altered feldspars, and often ar- 
ranged in the radial fashion just mentioned as showing in the quartz. 
In the case of the radiating quartz and ferrite clusters, it is often diffi- 
cult to tell if we are dealing with an alteration of a feldspar crystal or of 
unindividualized matrix, but in so many cases is it evident from the polar- 
ization effects that this alteration has progressed in orthoclase crystals, that 
it is reasonable to assume that the same is true for other sections present- 
ing a similar appearance. This quartz saturation varies in extent, but is 
8LS 
