118 ANCIENT REACH AT SAN PEDRO. 



Ancient sea beaches have been observed at a few points in or near the shore. In San Luis 

 Obispo county one well marked sea beach is found on the summit of a conglomerate hill which 

 overhangs the west side of the valley a little south of Corral de Piedras ; the summit height, 

 300 feet above the plain, was covered with fine quartz sand, mingled with broken and perfect 

 shells such as exist on the shore a little west, as the Saxidomus Nuttali, a common shell along 

 the coast. Another beach was found on the summit of a small hill which lies directly at the 

 mouth of the San Luis river on its southern side, with similar shells ; this hill had not an alti- 

 tude much exceeding 150 feet. The shells found on it were precisely similar to those found 

 along the present shore at the base. 



On the terrace, a few miles north of Santa Barbara, deposits of fine quartzose sand with the 

 broken shells indicated the existence of an ancient beach along its line, and similarly at the 

 port of San Pedro along shore, where the cliff has been cut down for the improvement of the 

 wharfage ; besides the terraced flat above, which may be 40 feet high, the cliff itself presents 

 the following section, from above downward : 



Alluvial clay and sand, 10 feet. 



Calcareous bed, (beach,) 8 feet. 



Arenaceous clay with modiolus, cardium, and small univalves, 22 feet. 



The strata dipping southwest. At another point north of the custom-house, a section slightly 

 different was obtained ; the distances between the two points might be 500 yards along shore, 

 the strata dipping north-northwest. 



Alluvium, 8 to 11 feet. 



Kaised beach, with shells, 4 feet. 



Argillaceous rock, 6 feet. 



Yellow and blue clays stratified, 30 feet. 



Accompanying the Venus Nuttali is a trocJdta, also very common along shore ; these two shells 

 form the mass of the perfect as well as of the comminuted shells of every raised beach along shore. 



