GEOLOGY OF PAJARO VALLEY. 37 



hills on the northwest were 1,500 feet high near their termination, while the Llomas Muertas 

 were not more than 300 feet high. At the junction of the Arroyo Pescadero with the Pajaro 

 diallage hornblende rock is exposed ; this is a spur thrown off from the Gavilan with a strike 

 north a little east ; west of this, on the right hank of the Pajaro, a stratum of limestone, meta- 

 morphic, and about thirty feet in thickness, is exposed ; it is a hard, dark, flinty rock, without 

 any fossils apparent. From the low hills described, the fossil Venus Fajaroana, (Conrad,) a 

 Miocene fossil, was obtained. As the beds containing Dosinia, whicti are found so plentifully 

 on the Salinas, were not observed here in relation with this fossiliferous bed, it is impossible to 

 connect the order of position. 



Leaving the Santa Clara valley, the Arroyo Bonito was crossed before entering the valley of 

 San Juan. This stream flows through a small valley bounded on the north by the termination 

 of the trachytic range, which formed the east side of the Santa Clara valley, and on the south 

 by the low hills alluded t >, which approach the river from each side, forming small hut beautiful 

 valleys, which are terraced on both banks. That on the right or east hank is somewhat higher 

 than the opposite one ; both extend along the river for eight miles, or so far as the valleys were 

 examined, and at the point where the river was first touched the height of the terrace was forty 

 feet ; a few miles further up it did not appear to be more than twenty feet, the river having 

 worn its valley down at the lower end ; the upper surface of the terraces were smooth, with a 

 few drift pebbles on the surface, but no beds of sand or apparent shore action. 



