!9 18 ] Davis: The Radiolarian Cherts of the Franciscan Group 309 



sils — ammonites and pelecypods. These shales are porcelaneous with 

 a smooth conehoidal fracture. Under the microscope, they -are seen 

 to contain numerous radiolaria, rather poorly preserved, together 

 with tiny fragments of clastic quartz, and specks of carbon. These 

 are all embedded in a fine siliceous paste, which remains dark between 

 crossed nicols. The plant remains are fragmentary and were prob- 

 ably drifted some distance from the shore. Their presence has been 

 accepted as proving the shallowness of the water in which the shales 

 were deposited. 



It is interesting to note the association of these radiolarian shales 

 with coarse sandstones and conglomerates of the Gondwana series. 

 Underlying these shales there are rather coarse sandstones. Immedi- 

 ately overlying the Sripermatur group are coarse, compact conglomer- 

 ates with sandstones and grits, apparently conformable on the lower 

 beds. The Gondwana series is believed to have been deposited, in 

 large part, by fluviatile action. Locally, however, rocks of unques- 

 tioned marine origin are intercalated with the continental deposits. 



EADIOLAEIAN EOCKS OF AUSTEALIA 



Certain radiolarian rocks of Australia which occur in association 

 with radiolarian cherts belong to the second class. These occur in 

 both the Silurian and Devonian systems of New South Wales. 47 



Radiolarian beds of lower Devonian are well developed near 

 Tamworth. The whole thickness of the radiolarian series is here at 

 least 9260 feet. It consists largely of jointed claystones which con- 

 tain numerous radiolaria. In these claystones the radiolaria consti- 

 tute about half the volume of the rock. In addition, cherty shales, 

 black radiolarian cherts, radiolarian limestones, coralline limestones, 

 and submarine tuffs, are interbedded with the claystones. No red 

 radiolarian cherts occur at Tamworth. 



The claystones which contain the radiolaria are dark brownish 

 gray to olive brown when fresh, but weather to a yellowish color. 

 They are usually quite soft and are very fine grained, all the particles 

 being less than .05 millimeter in diameter, and most of them ranging 

 from .025 millimeter to the size first mentioned. The claystones are 



47 David and Pittman, On the Paleozoic Eadiolarian Bocks of New South 

 Wales, Quar. Jour. Geol. Soc, vol. 55, p. 16. 1899. 



Hinde, G. J., On the Eadiolaria in the Devonian Eocks of New South Wales, 

 ibid., p. 38. 



Benson, W. N., Spilite Lavas and Eadiolarian Eocks in New South Wales, 

 Geol. Map., vol. 50, p. 17, 1913. 



Siissmilch, C. A., An Introduction to the Geology of New South Wales, 

 Sydney, 1914. 



