188 University of California Publications in Geology [Vol.7 



the same general territory as the lower sandstone — that is, east 

 of Sespe Creek, north of Santa Clara Valley, and does not cross 

 the Piru drainage basin to the east. It appears to die out before 

 the south side of the Santa Clara Valley is reached. 



These sands, then, are strictly local facies which grow thicker 

 as they approach the mountain mass to the north, from which 

 they were probably derived ; and to the west, south, and southeast 

 (to the east they pass under later formations and their extent 

 is unknown) they thin down either to negligibly small layers or 

 to complete extinction. 



Region South of Santa Clara Valley. — To the south of Santa 

 Clara Valley, the development of the Vaqueros-Monterey series 

 is simpler and the correspondence with the normal coast type 

 more readily discernible. Fossils are abundant in the lower 

 layers, so that the horizon is readily identified. The whole series 

 is thinner, in particular by loss of the Modelo sandstones and 

 a considerable decrease in the terrigenous shales. It may be 

 noted that these shales show variation in thickness on the north 

 side of Santa Clara Valley similar to that shown by the Modelo 

 sandstones, — that is. they decrease in thickness towards the south, 

 west, and southeast, although they do not, as far as observed, 

 entirely disappear. 



There appears to be no reason to doubt that the formations 

 south of the Santa Clara Valley represent as a whole practically 

 the same duration of deposition as do those to the north, and 

 that the particular differences of the latter are due simply to 

 an original position nearer inshore, during at least a large portion 

 of the period, and more directly related to a special soxirce of 

 supply of terrigenous detritus — the mountainous region of north- 

 ern Ventura County. This relationship was indeed suggested 

 as a possibility by Eldridge and Arnold: 17 "South of the river 

 this division does not appear to hold, yet one or another of the 

 characteristics of the Miocene, taken as a whole, north of the 

 river reappears on the south side, suggesting that the beds on both 

 sides of the valley from base to summit should be included in a 

 single formation." 



" Bull. 309, p. 21. 



