Lawson. I 



Host-Pliocene Diastrophism . 



These strands were identified by the writer at the following 

 approximate altitudes, viz.:— 1,240, 1,040, 960, 860, 700, 550, 400, 

 300, 240, 160 and 120 feet. 



The figures are given for the shore lines at the rear of the ter- 

 races or the base of the sea-cliffs. Since the terraces are, 111 many 

 cases, quite broad (one-quarter of a mile and more), these figures 

 are higher than those given for the same terraces by Mr. Davidson,* 

 who seems to have given the altitude for some point on the slope 

 of the terraces considerably below the horizontal line which marks 

 their abutment against the cliffs. 



Exceptional interest centers, of course, upon the highest terrace 

 of the series, since it affords us the measure of the total observable 

 uplift. This terrace, at 1,240 feet, is fortunately well supplied with 

 water-worn pebbles and mollusk borings in the limestone, so that 

 as a shore line its character is, like Caesar's wife, above suspicion. 

 The altitude of San Pedro Hill is given by the Coast Survey at 1,475 

 feet, but between the 1,240-foot terrace and the summit no evidences 

 of shore action could be observed, and the suggestion from the 

 facts is that 1,240 feet is the full measure of the uplift on this part 

 of the coast. It is possible, however, that San Pedro Hill may 

 have been completely submerged at a stage of the depression of the 

 coast of which we have here no record. It is also, possible that 

 more careful and prolonged search than the writer had time for, 

 may in future result in the discovery of traces of shore action 

 between the 1,240-foot terrace and the summit of this hill. 



The Record of Geological Events. — The facts observable at San 

 Pedro Hill warrant certain general conclusions, having a high 

 degree of probability as to the sequence of events on the coast in 

 late Tertiary and Pleistocene times. It is clear that San Pedro Hill 

 was, during the greater part of the process of the uplift, an island of 

 the Pacific. That is, it was a hill or isolated ridge which had earlier 

 been depressed Hill it was almost entirely, or possibly entirely, sub- 

 merged. This hill, giving due weight to the possibility of its being 

 essentially of structural origin, was undoubtedly shaped by ordinary 

 stream and atmospheric erosion. The rocks composing the hill 

 being of Miocene age and the lower flanks of the hill being mantled 



* Loc. cit. 



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