146 mr. a. j. jukes-beowke on [May 1906,. 



the case if both clay and flints have been derived from the solution 

 of the Chalk ; on the contrary, they become smaller and thinner, 

 with a surface-soil that is more crowded with flints, as we should 

 expect if these outer tracts had been exposed to detrition for a longer 

 time than those nearer to the main mass of the Reading Beds. 



It will also be noticed that the positions thus occupied by the 

 tracts of Clay-with -Mints quite preclude the idea that any great 

 thickness of Chalk can have been dissolved from beneath them 

 since the removal of the Reading Beds. It is true that, on the 

 Marlborough Downs, and to the north and north-west of Lambourn, 

 the Clay-with-Elints rests upon a lower zone of the Chalk than does 

 the main mass of the Eocene ; but there is good reason to believe 

 that the Eocene passed transgressively over the surface of the Chalk 

 towards the west, so that the Heading Beds stepped from higher to 

 lower parts of the Chalk as they spread westwards to and beyond the 

 present escarpment-riclge. 



North of the Thames Yalley the Clay-with-Elints behaves in 

 just the same way, rising along the Chalk- ridges with the Eocene 

 outliers, up to the summit-ridge of the Chiltern Hills. Farther 

 north, round Luton, it is associated with thick masses of brickearth 

 which seem to pass into loam and brickearth of Glacial age. 



I believe that much of the so-called ' Middle Glacial ' loam in the 

 counties of Bedford, Hertford, and Essex has been reconstructed 

 from the brickearths, which were themselves derived from Beading 

 Beds ; thus, near Weston, north-east of Hitchin, I have seen Clay- 

 with- Flints beneath loam, in a position which gave strong ground for 

 thinking that both passed under the neighbouring Boulder-Clay. 



Clay-with-Elints often wholly or partly surrounds outliers of 

 Beading Beds, or connects two such outliers, without descending far 

 below the level at which the local base of the Reading Beds is found. 

 In fact, if the loam and brickearth have been formed from the 

 disintegration of the Reading Beds, as is generally supposed : then 

 it seems impossible to avoid the conclusion that the formation of 

 the Clay-with-Elints was concomitant with that of the brickearths, 

 and also with the detrition and diminution of the Eocene outliers. 



Moreover, although but one colour is assigned to. such tracts on 

 the Geological Survey-maps, yet the index on the margin always 

 states that this colour includes ' Clay-with-Elints and brickearth ' 

 (or loam). Now, the brickearth, which is thus associated with the 

 Clay-with-Elints, is sometimes underlain by that material, but 

 sometimes rests directly upon the Chalk ; further, this brickearth 

 often includes beds or masses of quartz-sand. Hence, it is clear 

 that a theory designed to explain the formation of Clay-with-Elints 

 alone will not suffice ; it must be one that will account for the 

 disintegration, disturbance, and subsidence of masses of Eocene clays 

 and sands pari passu with the formation of the Clay-with-Elints. 



It must be recognized, in fact, that Clay-with-Elints is not a 

 distinct and definite material, like Boulder-Clay, which can be 

 separately mapped and receive an index-colour for itself: it is 

 inseparably associated with a more or less confused assemblage of 



