326 TJie Amenca?i Geologist. May, 1900 
one class of criteria at a time. Hence our general scheme must give 
in each order precedence to the predominating factor according to its 
taxonomic rank. Some of the most important criteria are the struc- 
tural features. C. R. Keyes. 
Erosion of Mountaix.s in Southern California.— While pass- 
ing through southern California with my father on our way to Siberia, a 
few days were given to study of the mountains of that region, to deter- 
mine whether they have been covered by glaciers as some have thought. 
With this end in view, we climbed one of the three highest peaks of 
southern California, Mt. San Antonio, or "Old Baldy" as it is locally 
called. This peak, although the lowest of the three, San Bernardino and 
San Jacinto being a little higher, rises to 10,083 feet and hence is a good 
place to look for signs of glaciationif such exist. A few of the observa- 
tions made in this region may be of interest to tlie readers of the A.vieri- 
can Geologist. 
Before reaching California, on the S :)uthern Pacific railroad the 
broad flat plains with gentle slopes rising to the foot of the mountains 
which project abruptly through them, as if thrown up and then half 
buried, attracted our attention. Towards the center of the valley the 
bottom is practically level and composed of fine sand. Nearer the 
mountains the material becomes coarser and coarser, also the grade is 
slightly steeper. A few miles from the mountains the material is a mix- 
ture of large sub-angular rock fragments to small well rounded pebbles, 
thrown together in heterogeneous confusion. 
It has been aptly said that this kind of valley has been formed by 
sheet erosion; for in this sub-arid region where cloud bursts are com- 
mon, especially along the mountain ranges, the whole valley is at times 
a sheet of water. This is of so general occurrence that the railroad 
company have raised their tracks from two to three feet and often put 
up a series of special ditches and embankments to protect against such 
floods, which have at times swept away two or three miles of track on 
an apparently level plain. 
The bed of the San Gabriel river, where the Southern Pacific rail- 
road crosses it, is a dry level valley but little lower than the surround- 
ing plain, which most of the year would scarcely suggest the existence 
of a rivei". 
The valley which extends inward to the east of Los Angeles is 
formed in a somewhat similar manner. It has been filled to at least a 
thousand feet with locally derived gravel and large boulders. A few 
wells have been sunk to 1,000 feet without striking rock, and the gen- 
eral character and heterogeneous mixing of different sized material 
continued the same from the top to the bottom. As this gravel furnishes 
much of the water for irrigation there are numerous wells of lesser 
depth, and all report the same conditions. From this it is evident that 
the original bottom of the valley is now below the present sea level, and 
is one of many indications of the comparatively recent subsidence which 
separated Catalina island with its mammoths from the main land. 
At the mouth of every canyon in the mountains along this valley 
