Yol. 62. ,] THE CLAY- WITH -FLINTS. 157 



of an anticlinal axis, while all traces of it have been swept away 

 over the central part of the arch and from its southern limb. The 

 reason for the persistence of such remnants on the northern side 

 only is also obvious from an examination of the maps (Sheets 300 

 & 316), for it is seen that this side has a very short drainage-slope 

 to the valley of the Eiver Itchen, the course of which is roughly 

 parallel to the presumed curve of the anticlinal axis. The southern 

 slope, on the other hand, is drained by a series of separate streams 

 which have long southerly courses, and the ground falls in this 

 direction to a much lower level than that on the north. Hence, 

 valley-erosion and general detrition of the surface must both have 

 proceeded more rapidly on the southern side, with the result that 

 all traces of the Claj^-with-Elints have been swept away, until we 

 approach the existing border of the Hampshire Basin, when we find 

 patches of it occurring at intervals just as if they had been outliers 

 of Heading Beds. The same is the case north of Chichester. 1 



VI. Summary and Conclusions. 



In the first place, it seems clear that the mass of the Clay- 

 with-Flints cannot have been derived from the Chalk. 

 Chemical analyses show that the quantity of insoluble residue in a 

 cubic foot of chalk is so small, that the residue left by dissolving 

 a cubic mass of Chalk-with-Flints in situ would not be a stratum 

 of Clay-with-Flints, but a bed of loose flints with some clay in 

 the interstices. More precisely, if the chalk dissolved was that of 

 the Micraster cor-anguinum-zone, and was 100 feet deep, the residue 

 would form a layer about 7 feet deep, consisting of 6 parts of flint- 

 nodules to 1 part of clay. Let such an accumulation be contrasted 

 with the real material, in which at least half the bulk is clay. 



Again, if we consider the clay alone, and regard a depth of 4 feet 

 of Clay-with-Flints as containing only 2 feet of clay, it would 

 require the destruction of 200 feet of chalk from the zones of 

 Marsupites and Micraster cor-anguinum to produce a layer of this 

 thickness, and it would be impossible to get it without a great 

 superabundance of flints ; for, although flints are fewer in the 

 higher zones, the insoluble residue in the chalk is also less. 



Lastly, it has been shown that, in areas where the Upper Chalk 

 evidently has suffered very greatly from solution and detrition, as 

 on Salisbury Plain, and especially over periclinal uplifts, there very 

 little Clay-with-Flints is to be found. 



On the other hand, there is strong evidence to show that most of 

 the material composing the Clay-with-Flints in the 

 districts examined has been derived from the Reading 

 Beds. These beds are an obvious source for the actual clay, and 

 all who have washed samples of it have found that it yields a residue 

 composed of grains of quartz and of ironstone, such as could not have 

 come from the Chalk. Of the larger ingredients, the green-coated 

 flints, rounded flint-pebbles, quartz-pebbles, and pieces of ferruginous 



1 See C. Reid, 'Geology of Chichester' Mem. Geol. Surv. 1903, p. 38. 

 Q. J. G. S. No. 246. n 



