no. 1617. NEW CRETACEOUS AND TERTIARY FOSSILS—ARNOLD. 349 
Fusus sanctecrucis, new species. ; Pleurotoma newsomi, new species. 
Galerus excentricus (?) Gabb. Pleurotoma perissolawvoides, new spe- 
Haminea petrosa Conrad. cies, 
Lunatia, new species, J. Pleurotoma sanctecrucis, new species. 
Natica oregonensis Conrad. Scala, species, A. 
Lirofusus ashleyi, new species. Sigaretus scopulosus Conrad. 
Pleurotoma, new species, a. Strepsidura californica, new species. 
Pleurotoma, new species, Db. Turcicula sanctacruzana, new species. 
CEPHALOPODA. 
Aturia ziczac Sowerby. 
Transitional Oligocene-Miocene.—The fine massive sandstones on 
Twobar Creek lying above the typical San Lorenzo (Oligocene) 
shales, but below the Vaqueros (lower Miocene) sandstone and con- 
elomerate, contain a fauna allied to those of both the beds below and 
the beds above. The fauna, however, appears to be more closely re- 
lated to that of the San Lorenzo. Among the species common to the 
latter and to the transitional beds are: Cardium cooperi Gabb, var. 
forenzanum, new variety; Marcia oregonensis Conrad; Tellina loren- 
zonesis, new species; Pecten sanctecruzensis Arnold; Solen, species; 
Yoldia impressa Conrad; Sigaretus scopulosus Conrad, etc. Those 
common to the transitional beds and the Vaqueros (lower Miocene) 
are: Marcia oregonensis Conrad; Chione (cf.) mathewsonii Gabb; 
Pecten brannert Arnold; Thracia trapezoides Conrad; Tritonium, 
species, ete. 
MIOCENE. 
Vaqueros sandstone-—The Vaqueros sandstone of lower Miocene 
age 1s one of the most important formations of the quadrangle. Its 
areal distribution is controlled largely by the northwest-southeast 
structural lines usual in the quadrangle, and the areas covered by it 
therefore consist for the most part of northwest-southeast bands. 
The sandstone varies in texture from fine-grained beds to con- 
glomerate, but are usually medium-grained and generally brown or 
buff in color, and vary from soft to extremely hard. The Vaqueros 
hes conformably above the San Lorenzo formation, and there is often 
a gradual change from one formation to the other, with no clear line 
of demarcation between them. But while the San Lorenzo formation 
is made up chiefly of shales and fine-grained, impure sandstones, 
the Vaqueros formation is composed principally of medium and 
coarse-grained sandstones, showing that the conditions of deposition 
were different during the two periods. 
The relation of the Vaqueros sandstone to the overlying beds is not 
so clear as are its relations to the underlying strata. There is an un- 
conformity west of a part of the Big Basin area between the diatoma- 
ceous shale (supposed to be Monterey) and the underlying San 
Lorenzo formation; the latter formation lies conformably below the 
Vaqueros sandstone. Elsewhere in the quadrangle there is com- 
