1915] Clark: Fauna of the San Pablo Group 409 



Feet 



Fine-grained sandstone 230 



Beds made up almost entirely of shells of Mulinia densata 3 

 Sbaly sandstone; contains Astrodapsis tumidus, subsp. cierboensis, and 



Astrodapsis pabloensis 100 



Medium-grained, partially laminated sandstone 360 



Conglomerate to pebbly sandstone 15 

 Light, massive, fossiliferous sandstone, containing Astrodapsis tumidus 



subsp. cierboensis, Scutella pabloensis, Mytilus coaling ensis, n. var. ? 250 



Massive, medium-grained sandstone 72 



Coarse sandstone and bands of fine conglomerate 100 



Massive sandstone and heavy conglomerates 50 



Coarse, soft sandstone 40 

 Coarse-grained sandstones with minor bands of conglomerate; Scutella 



gabbii zone 88 



Conglomerate, pebbles small and rounded 6 



2624 



(Unconformity ?) 

 Monterey Group. 



Scutella breweriana zone, mostly coarse conglomeratic sandstone. 



FAUNA 



The two major faunal zones found in divisions A and B, of the 

 San Pablo Bay section are also recognizable in the San Pablo group 

 on the south side of Mount Diablo. In the section in the vicinity of 

 Tassajero Creek there appears to be no marked lithologic change or 

 stratigraphic break between the two zones, but there is a very marked 

 difference between the faunas below and above a line which lies about 

 1400 feet above the base. Below this line Astrodapsis tumidus subsp. 

 cierboensis, Scutella pabloensis, Mytilus coalingensis, n. var.? Spisula 

 abscissa, Chrysodomus pabloensis and Calyptraea diabloensis are some 

 of the most common forms. Above this line and separated from the 

 lower fauna by only a few feet, Astrodapsis tumidus, Astrodapsis 

 whitney i, Pinna alamedensis, Mulinia densata, Tr option carisaensis are 

 found in abundance. 



The beds, in which the lower fauna is found, are here designated as 

 division A and those containing the upper fauna as division B. 



Division A. — The fauna of division A is divisible into two minor 

 zones, which are correlated with the two lower minor faunal zones 

 of division A of the San Pablo Bay section. Here also the division 

 is made on the basis of the sea-urchins. At the base of the group 

 Scutella gabbii is found; stratigraphically only a little above this, 

 Scutella gabbii disappears and Astrodapsis tumidus subsp. cierboensis 



