64 
LOWER BEDS OF THE SAN LOUIS VALLEY. 
of small fish—only the marks of the vertebrae and ribs were discernible—the scales of which 
had only been observed in the San Luis valley and elsewhere; intermingled were some fractured 
impressions of dorsal spines. In the same locality was found very beautiful impressions of 
pecten discus; lower down the strata became black from asphaltic impregnation. 
This description completes the history of these upper strata of the valley San Luis. In 
noticing them, as occurring in other places, reference is niade to this locality for a knowledge 
of their characters to avoid repetition. They are the most recent of the consolidated rocks of 
California; they have suffered the most extensively from denudation, and upon them, either on 
their edges or their slopes, the terraces and the raised beaches are found, and they are constantly 
associated with outflows of bitumen. 
Between the serpentine and trappean upheaval, on the east side of San Luis valley, and the 
conglomerates of the bituminous group on the west, the valley proper is located; the surface is 
covered with alluvial clays, the whole depth of which cannot he estimated, as no borings have 
been made, and not more than twenty feet of reddish yellow clays and light gravel were 
observed in the river courses. As the centre of the valley has suffered so much from denudation, 
it is probable that the ancient alluvium is also very deep. The valley, at present, slopes 
slightly to the northwest, where it opens on to the ocean, the direction doubtless which the 
denuded matter took when it was being removed from the plain. 
• A section of the valley is given on plate 7, fig. 2, and plate 1, fig. 2. 
In plate 7, the upper strata of the valley are illustrated. 
