12 GEOLOGY. 
striking than that afforded by the shell bed of San Pablo bay. At San Luis Obispo, a former 
sea beach, marked by accumulations of shells, such as now exist in the ocean below, runs along 
the bluff, some 80 or 90 feet above the present high-water mark. At San Pedro a similar 
accumulation of shells crowns the perpendicular banks near the landing, at an elevation not 
very different from that of the shell bed of San Luis Obispo. On the hills back from the landing 
other beds of shells indicate a still greater elevation of comparatively recent date; and marine 
shells are said to exist beneath the surface of many portions of the plain over which the road 
passes from San Pedro to Los Angeles. On this surface I found stones bored by Pholas; as I 
also did in the ancient sea bottoms at San Pedro, San Luis Obispo, and the bay of San Pablo. 
The alluvial plain to which I have referred, lying between Los Angeles and the Pacific, 
seems to have been formed at the mouth of Los Angeles river, when the ocean was at a higher 
level than now. By the subsequent elevation of the coast the stream has cut its way deeply 
into this plain, and now makes its exit many miles from its former mouth. 
At San Diego there are several beds of shells, having the same origin with those of San 
Pedro, but occurring at different elevations. Of these, the lowest, visible for a long distance 
on the north side of the Loma, lies but about twenty feet above the present ocean level, and is 
composed of a vast number of shells, of which some have not lost their colors. 
