30 



HAEHL AND ARNOLD — THE MIOCENE DIABASE. 



[Feb. 5, 



posited in water at least deep enough to be the habitat of lime- 

 forming organisms. The theory that most of the tuffs were depos- 

 ited in comparatively deep water is strengthened by the fact that 

 the fragments in most of the beds are angular, which would not be 

 the case had the tuffs been deposited near enough the surface of the 

 water to be affected by the action of the waves. 



Fig. lo. Section exposed along the Searsville-La Honda road one-fourth mile 

 north of La Honda, showing water-worn tuff interbedded between massive 

 angular tuff. 



Fig. lo shows a section which is exposed along the Searsville-La 

 Honda road a quarter of a mile north of La Honda. Interbedded 

 with the angular tuff is a layer of water-worn tuff about twenty feet 

 thick. The angular tuff appears to have been deposited in the sea 

 in successive layers until it reached near enough the surface of the 

 water to be affected by the wearing action of the waves, when the 

 water-worn layer was formed of the fragmental material. After a 

 time a submergence took place and the top of the deposit was again 

 lowered to such a depth as to be unaffected by the waves, or else 

 the volcanic ejectamenta filled up the shallow sea quite above the 

 water level. 



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Fig. II. Northeast-southwest section through the top of Mindego Hill, showing 

 the relations of the different tuffs exposed on it. 



