SANTA CLARA VALLEY: MODELO FORMATION. 
21 
fossil, the cast of a thin flat pecten, closely resembling Pecten pedroanus 
Trask (PL XXXVI, figs. 5, 6), lias so far been found in these shales; 
this was obtained in the outcrop immediately east of the road in Sul¬ 
phur Canyon, southwest of Bardsdale. This evidence, however, slip¬ 
py rts the suspected correlation, which otherwise is based on lithologic 
resemblances only. It might be well to say, furthermore, that the 
type locality of Pecten peckhami Gabb (PI. XXXI, fig. 3) is the Ojai 
Valley (probably in the shale on the south side) and that this species 
is unusually abundant in the Monterey shale in most regions where 
the formation is known. 
DIFFICULTIES OF CORRELATION BETWEEN NORTH AND SOUTH SIDES OF 
SANTA CLARA VALLEY. 
The division of the great series of beds north of the Santa Clara into the 
Vaqueros and Modelo is made easy by the abrupt and marked change in 
Jie character of the sediments at the contact of the lower Modelo 
* 
sandstone and the underlying shale. South of the river this division 
does not appear to hold, yet one or another of the characteristics of 
^he 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. The diffi¬ 
culty of correlation south of the river is greatly increased by the pres¬ 
ence of sharp folds and faults. For example, in the normal succession 
the siliceous shale and the “chalk rock'’ unquestionably overlie 
beds of altogether different character, identified as the Vaqueros; yet 
at the east end of Oak Pidge and in the western portion of the 
Santa Susana Mountains an equally heavy body of siliceous shale 
appears to dip beneath similar shale that is believed to be of lower 
Miocene age. This unusual succession may be attributable to fault¬ 
ing, the siliceous shale being the younger. On the other hand, it 
may possibly be that the siliceous shale capping Oak Ridge corresponds 
to the mass of siliceous shale that occurs as the uppermost of the 
Vaqueros beds in their type locality. In this case the Modelo would 
be entirely wanting south of the river. 
Another element in the difficulty of correlating the formations on 
opposite sides of Santa Clara River is the remarkable decrease in 
thickness toward the south. It would seem that the formations 
referred to have their type and maximum development north of the 
Santa Clara, and that south of the river the formations are thin, either 
through lack of material or through rapid changes in the attitude of 
the land, which resulted in intervals of nondeposition or even of ero¬ 
sion during the time the beds were being laid down. 
Bull. 309—07-3 
