266 University of California Publications in Geology [Vol. 7 



Cooper, in placing the species referred to Pot amides (?) 

 davisiana under this genus, which is confined to brackish water 

 or estuarine conditions, also leads one to infer that these strata 

 are estuarine deposits. One of the specimens shows that his gen- 

 eric classification, due to a superficial resemblance to Potamides 

 diadema Gabb is incorrect. The form referred to Potamides is 

 a Surcula. The formation of glauconite by deposition in the 

 tests of foraminifers, the occurrence of the genus Trochocyathus, 

 and of certain genera of Gastropoda and Pelecypoda indicate 

 that these beds are not in-shore deposits. 



Thompson and Murray 9 in discussing the bathymetric distri- 

 bution of glauconite state that — "it appears to be most abundant 

 about the lower limits of wave tidal and current action or in 

 other words in the neighborhood of what we have termed the 

 mud line surrounding continental shores. In the shallower depths 

 beyond this line, that is to say, in depths of about 200 and 300 

 fathoms, the typical glauconitic grains are more abundant than 

 in deeper water, but glauconitic casts may be met with in de- 

 posits in depths of over 2,000 fathoms. No typical glauconitic 

 sands have, so far as we know, been recorded in process of forma- 

 tion in the littoral or sub-littoral zones." 



Mosley 10 gives the range of Trochocyathus found at present 

 in the sea as from 100 fathoms to 750 fathoms. 



Vaughan 11 in his monograph on corals considers them as pecu- 

 liarly valuable indicators of bathymetric conditions of deposition. 



Tryon 12 gives the following ranges for some of the genera 

 of Gastropoda and Pelecypoda listed above. "The Cancellariae 

 from low water to forty fathoms," Tunis, low water to 100 

 fathoms; Corbula, lower laminarian zone to 80 fathoms; Dosinia, 

 low water to 80 fathoms ; Cardium, from sea shore to 140 fathoms ; 

 Nucula, 10-180 fathoms; Lcda, 10 to 180 fathoms; Turritella, 

 approximate range near 100 fathoms; Tapes, low water to 100 

 fathoms. The relatively small number of species of the genera 



a Challenger Report, Deep Sea Deposits, p. 378-391. 1891. 



10 Challenger Report, Zoology, vol. ii, pt. vii, p. 132. 1881. 



11 Vaughan, T. W., U. S. Geological Survey, Monograph 43, The Eocene 

 and Oligocene Corals of the United States, p. 23-33. 1900. 



12 Trvon, G. W., Structural and Systematic Conchology, vol. 1, 1882; 

 vol. 2, 1883; vol. 3, 1884. 



