396 University of California Publications in Geology [ VoL - 11 



the result of movements in unconsolidated sediments. This explana- 

 tion will not hold for these peculiarities exhibited by the Franciscan 

 and Monterey cherts, since in these rocks lenticular shale beds occur 

 where there is no evidence of shearing or displacement. 



Dixon and Vaughan 163 mention "wedge bedding," but they re- 

 garded it as produced by the contemporaneous erosion of beds of silt 

 and siliceous ooze, due to scouring of rather strong currents in shallow 

 water. The ideas of Dixon and Vaughan, regarding the lagoon 

 hypothesis, seem untenable, for various reasons pointed out on a 

 previous page. Even if the hypothesis be accepted, it is impossible 

 to explain this peculiar bedding by the scouring of currents: Current 

 scouring should not always confine itself to one horizon. It would 

 certainly result in cutting across several beds and result in sections of 

 the general nature indicated in the diagram (fig. 16). Nothing of 



Fig. 16. Eesult of current scouring in bedded silt and ooze. 



this sort has been observed in either of the formations of bedded chert 

 in California. The beds simply terminate at certain points without 

 evidence of contemporaneous erosion of any kind. 



Every stratum of mechanically deposited sediment is lens shaped. 

 If the shale partings in the cherts are mechanical sediments, and the 

 alternation is due to variations in currents, it would be expected that 

 the shales would occasionally show a lenslike termination. However, 

 the shales are very fine grained and must have been carried by gentle 

 currents, so that the area of such lenses would be large. As a result 

 we would expect the terminations to be rather rare, and found only 

 in an occasional section. In the Telegraph Canon section of the Mon- 

 terey cherts, east of Berkeley, there are at least a hundred termina- 

 tions of this kind observable in a single small quarry. In the plates 

 showing details of the bedding of the Monterey it will be noted that 

 there are numerous terminations of shale partings, even in the few 

 square feet covered by the photographs. Similar features are very 



163 The Carboniferous Succession in Gower, Quar. Jour. Geol. Soc, vol. 67. 

 p. 477, 1911. 



