:1()4 CLARK AXD ARXOLl^ MARTXE OLTGOCEXE 



this general horizon. This fauna is iiiueli better known in Oregon and 

 Washington than in California: the beds of this age in these northern 

 areas are not, as a rule, so highly folded and faulted, thus giving more 

 favoralile conditions for preservation. In California, on the other hand, 

 tlie stratigraphic relationships are more easily determined, due to the 

 semi-arid climatic conditions which have been tlie cause of better ex- 

 posure. 



FAUXAL ZOXES 



In Washington three fairly distinct faunas are found in the 10,000 feet 

 or more of sediments, which are considered of Oligocene age. These, be- 

 ginning with the oldest, will be referred to as the faunas of the Agasoma 

 acimiinatum ])eds, of the Molopophorus lincolnensis zone, and of the 

 Acila gettysburgensis zone. The stratigraphic ccjuivalent of these fauual 

 zones, as described by Arnold and Hannil)aL'' are the Sooke, San Lorenzo, 

 and Seattle formations respectively. The lowest of these faunas, that of 

 the Agasoma acuminatum beds or Sooke formation, has been found at a 

 number of localities in Oregon. "Washington, and Vancouver Island, and 

 in every place where the stratigraphic relationships could be determined 

 it is in beds below those of the Molopophorus lincolnensis zone. The two 

 faunas are very different, few species being common to the two. How- 

 ever, the beds containing this lower fauna appear to grade u]) into those 

 of the other horizon, and in no locality studied have the}' been found to 

 have any great thickness. For this reason it is probable that the former 

 fauna is a facies of the latter. Apparently the difference between the 

 fauna of the Agasoma acuminatum beds and that of the Molopophorus 



•^ Ralph Arnold and Harold Hauuihal : "The marine Tertiary stratigraphy of the north 

 Pacific Coast of America." Proc. Amer. Philos. Soc. vol. ."»2. 1015. pp. 573-580. 



These formational names were used by Arnold and Hannibal in a faunal rather than 

 a stratigraphic or lithologlc sense. Originally they recognized four divisions between 

 the Eocene and the Monterey — the Sooke. San Lorenzo. Seattle, and Twin River forma- 

 tions. C. E. Weaver has apparently shown that tlie beds forming the Twin River forma- 

 tion are a part of their Seattle formation, which has l^een repeated by folding. See 

 "The Oligocene of Kitsap County. Washington." Proc. California Acad. Sci.. 4th ser.. 

 vol. vi. no. 3. 1016. pp. 41-52. The name Agasoma acuminatum beds is used here for 

 the first time. As will he seen from the discussion further on in the paper, it Is still 

 doubtful whether the fauna in these beds belong to a zone distinct from the Molopo- 

 phorus lincolnensis zone. This latter name was first used by C. E. Weaver in his Ter- 

 tiary faunal horizons of western Washington. I'niv. Wash. Publ. Oeol.. vol. 1. no. 1, 

 1016. pp. 4-6. Weaver divided the fauna of the San Lorenzo, as recognized by Arnold 

 and Hannil)al. into two horizons, which he called the Lincoln and Porter horizons and 

 to which he also applied the names Molopophorus lincolnensis and Turritella porterensis 

 zones. Later work by Doctor Weaver and his students has shown that the faunas of 

 the Lincoln and Porter beds are much more similar than was at first supposed, and that 

 in all probability they are contemporaneous faunas. Thus only one faunal zone can be 

 recognized : for this it is agreed that the name ^lolopophorus lincolnensis zone should 

 be used. 



