Clark: The San Lorenzo Series of Middle California 61 



riam believed to be distinct from that found either in the shales or 

 in the sandstones of the upper division. This was referred to as the 

 fauna of the Agasoma gravida zone, and is the fauna of the beds 

 referred to the Oligocene in this paper. From the following extract 

 it will be seen that Merriam recognized the distinctness of this lower 

 fauna from that of the Scutella breweriana zone : 25 



The fauna of the lower division is much more characteristic than that of the 

 upper; that is to say, it differs more decidedly from that of the beds immediately 

 above and below it. . . . The most characteristic species are Agasoma gravida, 

 Dosinia mathewsoni, Chione mathewsoni, and Mytilus mathewsowi. These beds 

 rest upon the Tejon, which is very fossiliferous only a few yards below the 

 contact. A large percentage of the species in this horizon do not appear in the 

 upper Miocene and as yet not a single species has been found to extend down into 

 the Tejon. In- Contra Costa County the fauna of this zone is more distinctive 

 than that of the Monterey shale, considering even that the latter species repre- 

 sents a deep-water facies. 



Merriam, in the latter part of this paper, discusses the probable 

 correlation of the Agasoma gravidum beds with certain beds in the 

 southern part of the state, the horizon of which is known as the Tur- 

 ritella ocoyana zone, a part of the Lower Miocene. This will be 

 referred to more in detail in a later part of the paper, under the head 

 of correlation. 



Following Dall, the next publication in which marine Oligocene 

 is definitely referred to as occurring on the Pacific Coast was by Ralph 

 Arnold. Certain beds along the coast of the Olympic Peninsula, 

 which are uneonformably above the Eocene in that section, were 

 described under the name of Clallam formation, and referred to the 

 Oligocene-Miocene. He describes these beds as follows : 26 



Besting uneonformably upon the Eocene and older rock of the Olympic penin- 

 sula is a series of conglomerates, sandstones and shales rich in fossils and 

 extensive in occurrence. The formation is well exposed in the region between 

 Clallam Bay and Pillar Point, to the east, and for that reason is here named 

 the Clallam formation. According to Dr. Dall, the fossils of the formation 

 indicate that the basal portion of the series is Oligocene in age, while the upper 

 part is certainly Miocene. Since the separation of the two members will 

 necessarily have to be made on palaeontologic grounds and will require a more 

 detailed study of the material in hand than time has yet permitted, the term 

 ' ' Oligocene Miocene series ' ' will be used temporarily to designate the age of 

 the beds. A portion of the formation is unquestionably the equivalent of the 

 Astoria sandstones and shales occurring at the mouth of the Columbia river, 130 

 miles farther south. 



25 Op. cit., p. 378, 1904. 



2« Arnold, Ralph, Geologic reconnaissance of the coast of the Olympic Penin- 

 sula, Bull. Geol. Soc. Amer., vol. 17, p. 461, 190(5. 



