Vol. 4] Osfnont. — Geological Section of Coast Ranges. 



57 



four or five inches in diameter. No stratification is discernible, 

 coarse and fine material being indiscriminately mixed. This 

 formation lies unconformably upon the Franciscan, and beneath 

 the Sonoma Tuff, seemingly unconformably. These gravels do 

 not occur north of Healdsburg, so far as known, and have not 

 been looked for by the writer south of Trenton, though they 

 probably extend down to Porestville. On the east side of Santa 

 Rosa Valley they have not been encountered. No fossils having 

 been found in them, nothing definite can be said of their age, but 

 for certain reasons, which will be shown in the chapter on corre- 

 lation, they are supposed to correspond to the Orindan. Their 

 lack of bedding points to their being of Huviatile origin, and 

 they are probably quite local in occurrence. 



Sedimentaries beneath Andesite on Petaluma Creel- . — On the 

 eastern side of Petaluma Valley, near Penn's Grove, on the head- 

 waters of Petaluma Creek, are sandstones, shales and non-vol- 

 canic conglomerates of very similar appearance to those beneath 

 the Sonoma Tuff at Freestone and Tomales. This formation is 

 dipping at rather steep angles, 20° to 50°, and is overlain uncon- 

 formably by Mark West Andesite. No Sonoma Tuff was observed. 

 A fine grained clay shale yielded numerous good specimens of the 

 rare fossil Cyrena Calif omica Gabb. 



Lignitic Beds of Lawlor's Ranch. — About six miles southeast 

 of the locality above described, and five miles east of Petaluma. 

 on Lawlor's ranch, is a small bed of lignite in apparently these 

 same strata. The beds are folded at angles up to 45°, and lie 

 unconformably beneath the Mark West Andesite. A few inde- 

 terminable shells of fresh-water appearance, and several horse 

 teeth have been found. The teeth were submitted to Dr. J. W 

 Gidley of the American Museum, who kindly furnishes the fol- 

 lowing information reeardin^ them : 



"The last upper molar, specimen No. 2251, belongs to a spe- 

 cies of Neohipparion with a very progressive protocone. The 

 lower molar, with the same number, is a different individual. 

 This tooth has a peculiarly compressed appearance which does 

 not agree with the ordinary full proportions of the upper molar. 

 The little fold of enamel at the anterior external corner of the 

 protoconid proves lower tooth, No. 2251, to belong to a genus 



