Vol. 62.] THE CLAY-WITH-ELINTS. 143 



There is, however, another way of testing the probability of such 

 derivation, and this is to estimate the proportion of flints to clay 

 that would result from the solution of any given thickness of chalk, 

 for in the foregoing calculations the flints have been omitted. 



In the zone of Micraster cor-anguinum layers of flints are very 

 frequent, and scattered flints sometimes occur in the chalk between 

 them. In Kent and Sussex measured sections have shown that 

 layers of flints frequently occur every 3 feet, and that sometimes 

 they are only 2 feet apart ; records of borings also often mention 

 flints at intervals of 2 or 3 feet, but in the higher part of the 

 zone they are not quite so frequent. We shall probably be under- 

 estimating the quantity of flints, if we assume that their average 

 distance apart in the whole zone is 3^ feet • and if we also assume 

 that the average thickness of the flints is 3 inches, then every 

 14 feet of chalk will contain a depth of 1 foot of flint-nodnles, and 

 98 feet of this chalk will yield 7 feet of flints. 



In round numbers, therefore, the solution of 100 feet of Micraster 

 jor-anguinum-chalk will produce a layer of flints 7 feet thick, 

 together with enough clay to form a layer about 14 inches deep. 

 Hence there would be about six times as much flint as clay in the 

 mixture, and the product would not be ' clay-with-flints,' but a bed 

 of flints with about just enough clay to fill up the interstices between 

 the nodules. 



In the zones of Marswpites and Actinocamax quadratics the flints 

 are much less numerous. They do occur, however, in the latter 

 zone at distances of from 6 to 9 feet apart, and round the London 

 Basin flints are found in the Marsupites-zone, though sparsely. We 

 may perhaps estimate them as occurring in these zones at 8 feet 

 apart, but in quantity only enough to form a continuous layer 

 2 inches thick. At this rate there will be only twelve layers in 

 100 feet, with a total thickness of 2 feet of flints. The same thick- 

 ness of chalk, if composed of equal parts of the same zones, will 

 yield 9 inches of clay ; and in this we should have something more 

 like Clay-with-Mints, but still containing nearly three times as 

 much flints as clay ; whereas, in the real material, the proportion 

 is only 1 to 1. 



If we combine 100 feet of Marsujoites- chalk and 100 feet of the 

 Micraster cor-anguinum-zone, the 200 feet will yield a layer of 

 flints 9 feet deep and one of clay about 2 feet deep. The mixture 

 would be a clayey gravel, the proportion of clay to flints being nearly 

 as 1 to 4|. 



Y. Inferences to be drawn from the Distribution op the 

 Clay-with-Flints . 



From the conclusions arrived at in the preceding pages, it is clear 

 that the stratigraphical relations of the tracts of Clay-with-Flints, 

 both to the Chalk and to the Eocene Series, must be carefully 

 considered. In this connection, it is necessary to remember that 

 the Chalk had been raised and flexured to some extent before the 



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