Review oi Recent Geological Literature. 391 
a general survey of this region is made the formation below and 
above may be correlated and defined accurately as to local dips, 
'pinchings out' and other evidences of small unconformities." 
The remaining papers deal briefly with the geologic and eco- 
nomic resources of the territory as represented by their titles. 
J . w. B. 
Some Crystalline Rocks oi the San Gabriel Moantains, California. 
By Ralph Aknold and A. M. Strong. (Bull, of the Geol. Soc. 
of America, vol. 16, pp. 183-204, April 13, 1905.) 
This paper, by two students of the Leland Stanford Jr. Univer- 
sity, owes its interest in part to the location of the field of investi- 
gation. This is in a region of magnificent scenery, accessible from 
Los Angeles and Pasadena, well-known to tourists and but scantily 
investigated by geologists. It offers to petrographers a new and 
rich field of investigation. The results of preliminary petrographic 
study are presented in this paper. 
The San Gabriel mountains comprising an area of approxi- 
mately 1,200 square miles and located in southwestern California, 
extend CO miles southeast from the junction of the Sierra Nevada 
and the Coast range. The range is dissected by streams flowing 
east and west and is divided by the San Gabriel river into a south- 
ern portion with steep slopes and a northern range with more gentle 
slopes which grade into the Mojave desert. 
The geologic investigation of this region was made without topo- 
graphic maps and the rocks described were collected on reconnais- 
sance trips. 
A brief review of the previous literature on the region is 
given showing that there has been considerable divergence of opin- 
ion as to the age of the range. It has been called Primitive, 
post-Jurassic and post-Cretaceous. The presence of tilted lower 
Eocene sandstone and shale on the northern flanks of the range 
has led the writers to place the greater part of the elevation in 
late Eocene or Oligocene time. 
The petrography of the rocks of the San Gabriel mountains is 
given in some detail. The rocks are both igneous and metaraorphic 
and comprise biotite-granite, quartz-monzanyte, grano-dioryte, horn- 
blendyte, aplyte, micro-pegmatyte, quartz-hornblend-porphyryte, dia- 
base-porphyry, hornblende-dioryte-gneisses, biotite-granite-gneisses, 
hornblende-schists and garnetiferous-schists. Analyses are given 
of the grano-dioryte which is the most abundant rock type of this 
region as well as of the Sierra Nevada of California. The term 
grano-dioryte is used as defined by Lindgren: a rock in which lime- 
soda feldspars predominate and which consists of quartz, oligoclase 
or andesine or both, or orthoclase, hornblende and biotite, with ac- 
cessory titanite, zircon magnetite and apatite. Calculating the 
norm from analyses of the grano-diorytes, the reviewer finds the 
rock to be a biotitic-hornblende grano-aderose that is the rock is 
