1918] Davis: The Radiolarian Cherts of the Franciscan Group 297 



chert beds lie almost flat. In other places, though they are inclined, 

 they do not show the contortion which would be expected if they had 

 been greatly disturbed. The apparent relation in certain places 

 between degree of disturbance and the existence of bedded cherts 

 may be better explained on a mechanical basis. The bedded cherts 

 tend to show the greatest contortion because they are most incom- 

 petent, the alternation of hard and soft beds rendering them much 

 more susceptible to minor plication than the more massive diato- 

 maceous shales, which, while they may be thin bedded, are still much 

 more uniform in lithologic character. 



7. If cherts are due to changes, induced by metamorphism severe 

 enough to change soft diatoniaceous earth to jaspery silica, we would 

 expect the same action to change shales and limestones associated with 

 the cherts, which is not the case. 



8. Cherts show a peculiar branching of beds and a wedging out of 

 shale partings, before referred to. These would not be expected in 

 beds of organic ooze formed by skeletons of pelagic organisms, drop- 

 ping to the ocean bottom. Such beds should be of wide extent. 



Considering the black flinty cherts, that do not show such regular 

 bedding, they also do not appear to be silicification products, because 

 of certain peculiarities of the foraminiferal shells, that occur in con- 

 siderable numbers in them. In numerous instances the original cal- 

 cium carbonate of the shell still remains. In a few instances it has 

 been replaced by silica, and in some instances it has been leached out, 

 leaving the tiny mould in the midst of the chert. In those cases 

 where the lime carbonate of the shell is still preserved, it is fibrous 

 and is apparently in its original condition. In a few instances the 

 chambers of these shells are filled with opal; in many instances they 

 are filled with calcite ; in most cases they are found unfilled. 



One specimen collected by Professor Lawson from the Monterey 

 at Carmel, shows many of these foraminiferal shells in an excellent 

 state of preservation. The rock is black flinty chert, and in this 

 siliceous matrix the foraminifera are embedded. On breaking the 

 rock the fracture passes through these shells. The septa between the 

 chambers are perfectly preserved. The chambers of the shells are 

 empty. This specimen is cited particularly because of the numerous 

 well preserved shells which it contains. Similar examples, though not 

 so striking in appearance, are quite common. 



In view of the preservation of the foraminiferal shells, it is im- 

 possible to believe that such a rock could be due to silicification or to 



