278 The American Geologist. May, 1902. 
THE GNEISS SERIES. 
Aside from the intrusive Mesozoic granites, the older rocks 
of Los Angeles county occur in parallel belts having a gen- 
eral east-west trend. The first belt south of the Pelona schists 
is occupied by the gneiss series which has an average width of 
three miles and extends from the vicinity of Soledad pass to 
Texas canyon, a distance of about twenty-five miles. Three 
principal types of gneiss are represented which may be briefly 
described as follows: ; 
1. A light gray, fine-grained gneiss of quartz, white feld- 
spar and brown mica perhaps in part biotite. This phase is 
the commonest in the gneiss belt and has the appearance of 
being an altered ancient granite. In places it seems to have 
been partially fused and squeezed into neighboring crevices. 
2. A darker, more basic and coarser-grained variety. This 
appears to be in the form of dike-like masses irregularly dis- 
tributed through the light gneiss, suggesting that the relation 
of the one to the other is that of intrusion. The unsheared 
Mesozoic granites present a similar mixture of dark basic 
granite intruded by light acid granite; and, by shearing and 
intense metamorphism under heat and pressure, | can conceive 
their being converted into just such rocks as this gneiss 
series. However, the latter is very much older than the Mes- 
ozoic granites which intrude it as batholiths and dikes as well 
as narrow dikes of fine-grained gabbro and diabase, none of 
these later rocks being sheared. 
3. A singular, very coarse-grained sort of gneissic rock 
of dark gray color, characterized by aggregates of light pink 
and white small crystals seemingly of feldspar and quartz. 
They are surrounded by sometimes concentric bands of mica, 
quartz and feldspar like in the ordinary gneiss. Frequentiy 
the quartz-feldspar aggregates have perfectly round, eliptical 
or oval forms, and their borders are sharp. No mica occurs 
in these pebble-like portions. The most common form is the 
ellipse, when the major axis of each “pebble” in a given section 
has a common plane, but instances are observed of exceptions 
where a single elliptical “pebble” may vary 10° to 15° from the 
plane common to its neighbors. Where the “pebbles” are 
small they seem to have been generally squeezed and flattened, 
but the larger “pebbles” (one to two inches in diameter) seem 
