358 The American Geologist. June. 1905 
dipping 45° southwest. The rocks shortly become massive 
and are replaced by dark syenitic ones with an excess of 
hornblende. Two miles down, granite appears for a short 
distance, and in it a quarry has been opened. Gneissoid 
rocks soon replace the granite and these are followed by 
hornblendic rocks which vary from a schistose to a massive 
structure. In places they contain feldspars and pass into 
syenytes ; in others the rock is almost pure hornblende. 
The syenytes are followed by mica schists and these by 
coarse biotite granite about five miles above Howe [Fall- 
brook] station. In the granite are many pegmatitic veints, 
carrying biotite. garnets, and tourmaline. Fine-grained 
granite, varying at times to syenyte, forms the rock along 
the canyon for many miles below this point." 
Topography. The Fallbrook region is a Tolling plateau 
of from six hundred to eight hundred feet elevation. From 
Oceanside to within five miles of Pala, the San Luis Rey 
liver lies in a broad sandy valley. The mountains then 
close in for about two miles, making a narrow canyon, but 
at Pala the river valley opens out into a flat alkn ial plain 
from one to two miles wide, extending south-eastward to 
' the foothills at Rincon. Loose boulders and gravel strew 
the floor of this plain and of the small side valleys. The 
river keeps close to the south side of the valley and a few 
miles above Pala has cut a channel in this wash formation 
nearly one hundred feet below the floor of the plain. 
Veins and Dykes. The large intrusive dioryte areas 
are cut by veins composed chiefly of feldspar, biotite and 
black tourmaline. Many small veins also cut the granite 
area, but these contain only feldspar and biotite. without 
tourmaline. 
Two regions of apparently intrusive granite have been 
observed, the beryl region of Rincon, which will be de- 
scribed later, and a small area four miles soueheast of Fall- 
brook. At the latter place two prospect shafts have been 
sunk, one of six feet, the other of twenty-six feet in depth, 
on a pegmatyte vein in search for gems. This vein is 
about twenty inches wide, striking N.-S. and dipping 80° 
to the east. The vein is well defined from the decomposed 
country rock. It does not outcrop, but is marked by a local 
