544 W. A. Richardson — The Origin of Cretaceous Flint. 



flints corresponding to "granular zones" are common. In the 

 Jfarsupites and cor-anguinutn zones solid flints are the rule and 

 continuous flint bands are common. In the lower parts of the latter 

 zone carious flints become more common and prevail in the gracilis 

 and planus zones, where the flints are also spongiform, often 

 scattered, and immature. Thus the opening and closing phases of 

 the sequence are characterized by enfeebled flint development as 

 well as by a wide interval between the bands. 



It may be mentioned that such types as banded flints, paramoudras, 

 and flint rings present less difficulty when considered as rhythmic 

 phenomena, and some of them have already been imitated in gels. 



Devon Derset. Sussei ftent rtotfolh Yor 



Fig. 4. — Horizontal distribution of Flint in the Chalk. 

 (The zonal numbers are the same as those used in Fig. 3.) 



If the distribution of the flint be studied in a horizontal section, 

 such as that given in Fig. 4, some rather interesting relations are 

 brought to light. In drawing the section the Chalk has been 

 reduced to a horizontal base. The zonal boundaries are shown in 

 dotted lines. The chain-dotted lines represent the upper and lower 

 limits of flint occurrence and the approximate line of its maximum 

 development. 



Now it will be apparent that the lines of flint development 

 transgress the zonal boundaries. If the flint had been deposited 

 contemporaneously with the Chalk, one would expect it to conform 

 horizontally to the zones, and its failure so to do strongly supports 

 the view that the flint is later in date than the deposition of the 

 Chalk. 



There is, moreover, a curious but rather striking tendency of the 

 flint development lines to follow the present surface of the Chalk. 

 If the flint bands are due to periodic organic growth, or to periodic 

 chemical precipitation, there is no reason why its horizontal distribu- 

 tion should show such a characteristic. On the other hand, if we 

 suppose the present surface to be related more or less remotely to the 

 surface at the time of uplift, it would mean that the lines of flint 

 development were also related to that surface. Such behaviour is not 

 merely in conformity with the theory of rhythmic precipitation of 

 solutions diffusing through the Chalk under draining actions due to 

 uplift, but might be predicted as a result to be expected of such action. 



