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University of California. 



IVOL. U 



disappear, but the marks of the boring mollusks would remain, to 

 testify to their former presence. Locally, also, owing to certain 

 special conditions, the lower cliff might have receded so rapidly as 

 to entirely obliterate the terrace. The lower and upper cliffs would 

 then appear as one, and, as a single cliff, might have encroached 

 upon the land beyond our elevated shore line.* Thus we have 

 before us the characteristics of the sea terrace which would be pre- 

 sented for inspection if the present shore line were to be elevated 

 100 feet, viz., a narrow plateau-like shelf, gently sloping seaward> 

 limited in the rear by a strictly horizontal line (the shore line), 

 above which would rise a somewhat softened sea-cliff 100 to 200 

 feet, and in one place 300 feet, high, and limited in front by a more 

 vertical cliff rising above the new shore line. On this shelf would 

 be strewn bowlders and pebbles, chiefly in the embayments, and 

 in the soft, fine-grained rock of which the hill is composed mollusk 

 borings would abound. Had the rock been hard or unequally 

 resistant, occasional, conical stacks would rise above the otherwise 

 even slope of the terrace. Precisely these features characterize the 

 terraces which score the slopes of San Pedro Hill so notably. 

 Every terrace is a shelf cut into the rocky slope, beveling the 

 upturned edges of the strata. Every terrace has a cliff rising 

 steeply from its rear, the intersection of the plane of the terrace 

 and that of the cliff being a strictly horizontal line, as near as the 

 eye can judge. Every terrace falls away with varying degrees of 

 definiteness into the cliff of the next terrace below. Every terrace 

 has a gentle seaward slope, which is inherent in its rocky floor, and 

 not due essentially to alluvium. The terraces are strewn sparingly 

 with pebbles and water-worn bowlders of moderate size. Mollusk 

 borings are plentiful, and were observed by the writer on several 

 of the terraces up to an elevation of 1,240 feet above sea level. 

 Terraces having these characters are clearly ancient ocean strands, 

 and the suggestion that they are due to the abrasion of moving ice 

 is, therefore, absolutely negatived. 



*For a fuller account of the development of sea-cliffs and other shore fea- 

 tures, consult Gilbert's "Lake Bonneville," U. S. G. S. Monograph I. It 

 should be noted, however, that certain features associated with the develop- 

 ment of sea-cliffs, and given by Gilbert as criteria for the recognition of sea- 

 cliffs of lakes, are, as a rule, not available for this purpose on oceanic coasts. 



