NEOCENE STRATIGRAPHY. 319 



gasteropod beds run all the distance and quite uniformly 

 three feet apart. Their own thickness, however, varies 

 from one to five feet, while the beds overlying them are 

 entirely different in different parts of the course. 



The section was made by pacing (corrected by map), 

 the minor layers being estimated by rough measurement 

 or by eye. Frequent landslides at the foot of the bluff 

 make it difficult to get accurate measurements of many 

 of the layers. At Wood's Gulch there was found to be 

 a fault of 825 feet, downthrow on the south side. This 

 was the only fault of any magnitude discovered, except 

 those at the south end which could not be measured. 

 Professor Lawson estimated the same strata to have a 

 thickness of 5626 feet.* These beds appear to thin out 

 to the southeast. 



This section was the only one obtained, since the strata 

 in the sections south of Point San Pedro have, as a rule, 

 low dips and would require instrumental surveys to assure 

 any degree of accuracy. 



A little south of Point Montara this formation lies upon 

 the granite. The lowest bed where it lies close to the 

 granite is almost made up of pebbles and boulders of 

 granite. In a short distance the proportion of granite 

 rapidly decreases and the layer becomes very fossilifer- 

 ous, gasteropods predominating, and from their resem- 

 blance to those of the lower gasteropod beds of the sec- 

 tion on Seven-Mile Beach it is thought the two belong to 

 the same horizon. 



In the long hill at Point Pillar, the strata are excellently 

 exposed dipping south, the dip being as high as 40^ part 

 of the distance. The same rock, the drab argillaceous 

 sandstone with red joint faces, runs through the whole 



*Uuiv. of Cal., Bull. Dept. Geol., vol. i, p. 147. 



