392 University of California Publications in Geology [Vol. 11 



sion opposite the mouths of large rivers, nor are they unusually nar- 

 row at those parts of the shore line where there are no streams. 

 The conclusion is forced upon us, that they are transported by ocean 

 currents and distributed by them all along the coast. For this reason 

 alternation of high river stages with stages of low water would have 

 little effect in determining the ultimate position of deposition of the 

 finer sediments, or in producing rhythmic bedding in any terri- 

 genous muds. The final disposition of material depends upon ocean 

 currents, which are in all probability independent of climatic cycles. 



The hypotheses of climatic variation are also opposed by the 

 occurrence of both cherts and shales in lenticular beds, or in nodules. 

 Such features could not be produced in fine sediments carried by the 

 action of gentle currents. 



Two other hypotheses have been suggested by Lawson and 

 Palache. 160 



Rhythm in Growth op Radiolaria 

 If the cherts could be accepted as being radiolarian oozes it is pos- 

 sible to explain the alternation as due to a periodic variation in the 

 growth of the radiolaria. It is known that diatoms show a periodic 

 variation in development. The work of Raben, before referred to, 

 showed two maxima per year in the number of diatoms in Kiel Bay. 

 These variations, however, were very short in period, and it seems 

 unlikely that they could result in the observed alternations. Such an 

 assumption would lead to an improbable conclusion regarding the 

 rate of accumulation. 



A further objection has been referred to before. Core samples 

 of radiolarian oozes show no evidence of such bedding. Neither is 

 such an alternation shown in the Barbados earth. 



Rhythm in Siliceous Springs 

 If the idea of siliceous springs as a source of the silica were 

 proved, it is conceivable that there might be a rhythmic variation in 

 the supply of silica from these springs, so that one would get periods 

 of silica precipitations alternating with periods of ordinary sedimenta- 

 tion. Here again, though the idea seems improbable, there is not 

 much evidence either to prove or disprove it. However, it is said that 

 the siliceous waters in Steamboat Springs, Nevada, show a variation 

 in flow, dependent on rainfall. 



leo The Berkeley Hills, Univ. Calif. Publ., Bull. Dept. Geol., vol. 2, p. 445, 1901. 



