580 ARNOLD AND HANNIBAL— MARINE TERTIARY [April 19, 



It is therefore convenient to use the name San Lorenzo here as 

 well as in California. 



On the North Pacific Coast the San Lorenzo ordinarily con- 

 sists of two members ; a basal sandstone and conglomerate varying 

 from 10 to 500 feet or more in thickness and composed largely of 

 worked over volcanic ejectmenta, lying on the basalt or andesite flow 

 which at many points marked the opening of the Astoria epoch, or 

 directly on older rocks ; and a shale member several thousand feet 

 thick ordinarily arenaceous, gray and massive, less frequently ashy 

 and dark colored, or calcareous and bluish. Seen under the micro- 

 scope this shale is composed largely of fine volcanic detritus and has 

 little of the organic character of the San Lorenzo shale of California. 



The principal areas of the San Lorenzo formation on Vancouver 

 Island form the narrow intermittent strip of Oligocene sandstones 

 and shales bordering the southwest coast from Sombrio River west 

 to Barkley Sound. In Washington the conglomerates of the Cape 

 Flattery section and eastward to Shroud Head ; the sandstones and 

 shales overlying the Oligocene basalts and andesites south and west 

 of Port Townsend ; the sandstones overlying the lower Astoria 

 l)asalts west of Port Orchard Sound and forming the lower half of 

 the Bainbridge Island section of the Seattle Monocline ; the shales 

 overlying the basal Astoria basalts north and east of Oakville, 

 Porter, and Elma ; the lowest Oligocene exposed in the Lincoln Creek 

 :section ; and a large part of the monocline previously mentioned 

 as occurring west of Winlock including the Winlock, Pe Ell, Hol- 

 comb, Skamokawa and Upper Nasel River exposures are note- 

 worthy. In Oregon the Astoria shales south of the Columbia River 

 at Clatskanie, Scapoose, the upper Nehalem Valley, and West Dairy 

 Creek, isolated exposures about the borders of the Willamette Valley 

 at Silverton, McCoy, and overlying the Eocene basalts at Eugene 

 and Springfield, the lowest beds of the westward dipping monocline 

 between Blodgett and Newport, and the steeply dipping section 

 exposed in the seaclififs south of the entrance to Coos Bay between 

 Basendorfs (Miner's Flat) and Tunnel Point should be regarded as 

 contemporaneous. The so-called Pliocene of the Yahates River 

 belongs also to this horizon. 



