no. 1617. NEW CRETACEOUS AND TERTIARY FOSSILS—ARNOLD. 851 
ie 
The formation consists chiefly of dintonneesorne shale, with here and 
there intercalated sandstones. The diatomaceous nal occurs 1n 
various grades of purity, from the very light shales composed almost 
entirely of diatom skeletons to those containing such large propor- 
tions of clay and fine sands as to almost or quite lose their diatoma- 
ceous character. In the region northwest of Santa Cruz and in 
many other places in the Coast ranges the Monterey shale is ordi- 
narily spoken of as “chalk rock.” The shale usually weathers to 
white or buff color, but unweathered surfaces often present a dark 
gray, drab, or chocolate color. 
The paucity of marine invertebrate fossils in the formation is one 
of its characteristics, although the rather widespread distribution of 
two of its species, Pecten peckhami Gabb and Arca obispoana Conrad, 
is important. 
The following species have been found in the Monterey at various 
points throughout the quadrangle: 
List of Monterey, middle Miocene, fossils in the Santa Cruz quadrangle. 
ECHINOIDEA. 
Cidaris, species, a. 
’ PELECYPODA. 
Area obispoana Conrad. Pecten peckhami Gabb. 
 Chione mathewsonii Gabb. Semele, species, a. 
Corbula, species, da. Siliqua, species, a. 
Diplodonta (aff.) serricata Reeve. Tellina congesta Conrad. 
Mactra montereyana, new species. Venericardia montereyana, new spe- 
Marcia oregonensis Conrad. cies. 
Pecten andersoni Arnold. Yoldia impressa Conrad. 
GASTEROPODA. 
Huminea petrosa Conrad. 
Santa Margarita formation.—The region of Scott Valley north of 
Santa Cruz is occupied by a formation showing some very distinctive 
characteristics. The base of this formation, which in places rests 
unconformably on the Monterey, consists of about 200 feet of coarse, 
white, incoherent sand with bedded conglomerates near the bottom. 
Above the white sand is a thickness of about 100 feet of fine, thin- 
bedded, rather hard shale, which in the Scott Valley region lies nearly 
Horizontal | 
Few fossils have been found in either the sandstone or shale of 
this formation, but the lithologic similarity of the beds to those of 
the Santa Margarita formation of the Salinas Valley, together with 
the identity of those species of fossils which have been obtained from 
the Santa Margarita in the Santa Cruz region, has led to the corre- 
lation of the latter with the typical Santa Margarita paatner south. 
