594 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



locality is on the western spur of a hill, whose elevation is 

 296 feet. The limestone outcrop occurs at an elevation of 

 400 feet, which point is near the west line of the section, 

 about 150 feet above the wagon road which cuts the north- 

 western corner of Section 16. The exposure is about a hun- 

 dred yards long and 35 to 40 feet in width. There is a three- 

 foot stratum of limy conglomerate in the middle of the sec- 

 tion. A small amount of development work had been done 

 on the exposure when the writer visited it on May 18, 1918, 

 and it seems entirely probable that the deposit will yield a 

 tonnage sufficiently large to warrant exploitation. The hills 

 to the north across the valley were carefully examined, but 

 the outcrop does not extend in that direction. The hill to the 

 east was also examined, but no outcrop was discovered. The 

 northern end of the deposit stops quite abruptly and the 

 writer is inclined to think that a cross-fault may terminate 

 the deposition to north. The southerly extension of this de- 

 posit disappears gradually as one descends the hill slope. A 

 cross-cut should be made at the southern end to determine 

 whether this gradual disappearance is due to a lense structure 

 or merely to a thickening of the soil cover at that place. 



Another deposit occurs on the Jacobsen ranch, near the 

 southeast corner of the northwest quarter of Section 9. An 

 old limekiln at this place, long abandoned, shows that this 

 deposit was opened years ago. The limestone at this place 

 is too gravelly to be of value even as a source of ground 

 limestone. Another small deposit occurs in Section 17 on the 

 west side of the Point Reyes-Petaluma-Red Hill road, but the 

 deposit is cut off by serpentine and schist and has apparently 

 been intruded by the serpentine. The deposit is too small to 

 be economic. All of these occurrences of limestone are close- 

 ly associated with typical cherts and schists of the Fran- 

 ciscan group, and the writer has assigned them to it on this 

 account. The limestone deposit in Section 16 is an unusual 

 type of rock in that it is associated with conglomerate and 

 appears to be a beach deposit. Certain obscure markings in 

 this limestone suggest that it is composed of comminuted 

 shell fragments. The deposit should be carefully searched for 

 fossils. 



