1918] Davis: The Radiolarian Cherts of the Franciscan Group 251 



in thickness of adjacent beds of chert and shale, the disturbance in 

 bedding dies out quickly. In some instances, a chert bed may die 



Fig. 5. Occurrence of minor lenses of chert. 



Fig. 6. Occurrence of chert in a chain of nodules. 



Fig. 7. Nodule of chert lying between ends of two beds. 



away for a short distance, and its place may be taken by a little chain 

 of separated chert nodules. In other cases a chert layer simply ends, 

 and the shale partings on either side come together again as shown 

 in figure 8. These occurrences illustrated in this last figiire are ex- 



Fig. 8. Termination of a chert bed. 



tremely common and may be found by careful examination of almost 

 any section of the chert. In some places, large numbers of lenslike 

 masses having the relations illustrated in figure 9 and plate 28b, may 

 be observed in a section having an area of only a few square feet. 

 The terminations are not always wedgelike, as indicated in some of 



