B48 PROCEEDINGS OF THE NATIONAL MUSEUM: vou; X¥x1¥. 
OLIGOCENE: 
Probable lower Oligocene sandstone.—This fommmation | is composed 
of medium to coarse-grained massive brown and buff sandstone, anid 
outcrops in a ‘slarneullaye area, the éastern portion of which is ot the 
San Lorenzo River 4 miles north of the town of Boulder Creek. It 
attains a maximum thickness of at least 2,100 feet, and as the base of 
this section was not exposed it is probably some thicker. The forma- 
tion conformably underlies the San Lorenzo shale, but its base is un- 
known, unless it is represented by the upper member of the uncon- 
formity exposed immediately south of the mouth of Pescadero Creek. 
No fossils have been found in the main area of the formation, but 
the outcrop near the mouth of Pescadero Creek has yielded several 
forms, aniong which are Pecten, closely allied to P. sanctwecruzensis 
Arnold, a fragment of a huge Venericardia, a large Turritella, and 
an echinoderm suggesting Clypeaster. 
San Lorenzo formation—The San Lorenzo formation, within the 
limits of the Santa Cruz quadrangle, is characteristically of shale 
and fine sand. It outcrops in the region north of Ben Lomond 
Mountain and between the latter and Castle Rock Ridge, its areal dis- 
{ribution being controlled by the northwest-southeast folds which are 
the prominent structural features of this portion of the quadrangle. 
The formation attains a maximum thickness of about 2,500 feet on 
Kings Creek. The most abundantly fossiliferous localities are on 
the San Lorenzo River, Kings Creek, and Two Bar Creek, and also 
along the south side of the Big Basin. The following fauna has 
been obtained from the San Lorenzo in various parts of the Santa 
Cruz quadrangle: 
List of San Lorenzo, Oligocene, fossils from the Santa Cruz quadrangle. 
ECHINOIDBA. 
Cidaris branneri, new species. 
PELECYPODA,. 
Oardium cooperi Gabb, var. lorenza- Nucula dalli, new species. 
num, new variety. Pecten peckhamé Gabb. 
Cardium, species, a. Pecten sanctecruzensis Arnold. 
Leda, new species, s. Phacoides, species, a. 
Lithophaga, species, a. Solen, species, a. 
Malletia chehalisensis, new species. Tellina albaria Conrad. 
Modiolus ynezianus Arnold. Tellina lorenzoensis, new species, 
Mulinia, (2?) species, «. Tellina, new species, a. 
Neewra, new species, a. Yoldia impressa Conrad. 
GASTEROPODA. 
Actwon, species, A. Dentalium substriatum Conrad. 
Architectonica lorenzoensis, new spe- Lusus corpulentus Conrad. 
cies. Fusus geniculus Conrad. 
Dentatium, new species, U. Fusus hecowvi, new species. 
