292 CALIFORNIA ACADEMY OF SCIENCES. 



DETAILED STRATIGRAPHY. 



In a more detailed study of the stratigraphy, the form- 

 ations will be taken up from earlier to later. The meta- 

 morphic sandstone will be considered as at least a more 

 or less marked facies of the pre-Miocene sandstones. 

 The future will decide whether it be simply a metamor- 

 phic facies of the lowest bed of the great series which 

 have been known as the San Francisco sandstone, or 

 whether this term has been applied to beds differing not 

 only in age, as it is quite probable that they do, but in all 

 their structural relations. The evidence observed will be 

 given under the relations of the Pescadero series. 



LIMESTONE. 



Lithology. — 'X'his bed of limestone is in places highly 

 crystalline, in other places it does not appear to be so 

 much inetamorphosed, and contains long lenticular masses 

 of chert through it in the direction of dip. Prof. Whitney 

 describes it in one place as follows* : " The upper layers 

 are thin bedded, and some strata are light colored, others 

 dark; below the stratification is less distinct, the layers 

 heavier and the rock more crystalline." 



The evidence would seem to indicate that there are two 

 layers, both of considerable thickness. One of the layers 

 is probably not less than 300 feet thick, a section on Per- 

 manenta Creek giving much more than that, but with such 

 poor exposures over part of the outcrop that the section 

 was not considered reliable. Whitney estimated at one 

 place that it " must be over 1000 feet in thickness." t 



Dish'ihution. — This limestone was observed in large 

 masses in only a few places; one in the Calera Valley, 

 where it caps some small knolls; and again on the ridge 



* Geol. Surv. of Cal., Geology, vol. i, p. 75. 

 t Geol. Surv. of Cal., Geology, vol. i, p. 75. 



