14 



Physiography 



jy#wUah>>Ai^iN»MkJL.aNMii. ».*%«*^ ^ 



Figure 9. Boulders of Eocene sandstone 0.3 mile north of Scripps Pier, La Jolla. Fittings and stone lace have been 

 developed by chemical and biochemical weathering. Difference in positions of boulders in July 1940 (top) and August 

 1956 (bottom) shows considerable movement by waves during this period. 



capable of evaluation is the much quoted 

 compression and expansion of air trapped 

 in caves or open joints by rising waves. 

 Where a small opening reaches to the ground 

 surface, the compressed air forces water 

 spray upward as a geyser-like spouting horn. 

 More commonly, the compressed air drives 

 the spray nearly horizontally seaward out of 

 openings that have become filled with water. 



Many examples of the latter form of air 

 compression are known in southern Cal- 

 ifornia, and good spouting horns exist at 

 one or two places on the mainland and on 

 all islands except possibly San Miguel and 

 San Nicolas. Spouting horns are spectac- 

 ular, but they are by no means convincing 

 evidence of the erosive ability of com- 

 pressd air because many have lasted for at 



