1918] Davis: The Radiolarian Cherts of the Franciscan Group 361 



idea, the doctrine of permanence of ocean basins cannot be used as 

 an argument against the abyssal origin of the radiolarian cherts. In 

 so far as it is based on independent considerations, such as concep- 

 tions of isostatic balance, it may make us cautious about accepting 

 the idea of the abyssal origin of radiolarian cherts. As Chamberlin 126 

 has shown, most of the deposits which are suspected to have an abyssal 

 origin are in such geographical locations that their interpretation as 

 abyssal deposits need not come into conflict with any hypothesis of 

 permanency of ocean basins. Most of the occurrences of such rocks 

 are near the margins of continents, and one may think of them as 

 situated on blocks of the earth's crust intermediate between well 

 defined oceanic blocks and well defined continental masses. It would 

 then be possible to regard them as carried down at one time by the 

 relative subsidence of the ocean block, and again at a later time, 

 raised with the continental mass. We might then believe, that while 

 the cherts were abyssal, they were still laid down near land and 

 partly within the zone of terrigenous deposition. The occurrences of 

 the radiolarian rocks in England, Scotland, Barbados, Solomon 

 Islands, New Zealand, Australia, Borneo and the Malay Peninsula 

 and Archipelago, California Coast Ranges and Alaska, satisfy this 

 recpiirement. The occurrence of identical cherts in the Urals, in the 

 Alps, in the Sierra Nevada of California, and in the Peshastin forma- 

 tion in the state of Washington, causes the conception of permanence 

 of ocean basins and the interpretation of radiolarian cherts as abyssal 

 deposits, to come into decided conflict. Even in the absence of much 

 evidence of a positive nature against the idea of abyssal deposition, 

 one would feel hesitant about ascribing to the cherts a deep sea origin. 



Significance of Carbon. — The presence of carbon, in certain shales 

 interbedded with the Franciscan cherts, has been alluded to. The 

 radiolarian cherts of the Malay Peninsula also contain considerable 

 carbon and carbon is reported in many other occurrences. The pres- 

 ence of carbon has been cited by Scrivenor as evidence of shallow 

 water deposition. It does not seem to the writer that this criterion is 

 valid. On the suggestion made above — deposition in deep water not 

 far from shore — conditions would be favorable for the inclusion of 

 considerable carbon in the deposits. Agassiz 127 dredged up leaves, 

 bamboo, sugar cane, and similar material from the ocean bottom in 

 water 1000 fathoms deep, at a distance of ten miles from certain 



12(1 Chamberlin, T. C, Diastrophism and the Formative Processes. V The 

 Testimony of the Deep-Sea Deposits, Jour. Geol., vol. 22, p. 131, 1914. ' 

 127 Qp. ext., vol. 1, p. 291. 



