148 MR. A. J. JUKES-BROWNE ON [May I906, 



of pebbles. There are several exposures of similar clay on the 

 outlier of Heading Beds at Maiden Grove (Oxon). I have the same 

 authority for stating that most of the Beading-Bed outliers, which 

 occur among the Clay-with-Flints of the Berkshire Downs, are 

 overlapped at their edges by clay and loam with angular flints. 

 The flints in such clays are almost always white and angular 

 unbroken flint-nodules being rare ; but he believes the material to 

 be continuous with the surrounding Clay-with-Flints. 



Mr. White has also noticed that this transgression of the Clay- 

 with-Flints onto Eocene tracts occurs most frequently on the sides 

 which face up the slope of the Chalk-surface, and much less often 

 on the lower or dipward side of the outliers ; a fact which suggests 

 a certain amount of slow movement from the main watershed. 



The intimate relation between the occurrence of Clay-with-Flints 

 and the basal plane of the Eocene Series is brought out still more 

 strongly by a study of the area which lies between the London 

 and Hampshire Basins. There is a further advantage in dealing 

 with this area, in the fact that the geological mapping of it has 

 been completed, and published on the new series of 1-inch maps 

 (Sheets 282, 283, 284, 298, 299, & 300), so that these can be 

 referred to in confirmation of the statements made below. 



In considering this area, we must remember what has been said 

 on p. 144, that the structure is complex, and that the flexuring was 

 not all produced at one period ; that the main broad geanticline is 

 of pre-Eocene date, and was planed down before the Reading Beds 

 were deposited, both Chalk and Eocene being subsequently bent 

 into smaller and narrower folds. 



Beginning with the western part of the area (Sheets 282 & 298), 

 we find that these include a surprisingly-small amount of Clay-with- 

 Flints. In the far west, and just outside the limits of Sheet 282, 

 there is a tract of some length on the highest ridge of the downs 

 which lie between Imber and Warminster. On the north, there 

 is a curvilinear tract on the summit of the downs south of Chirton 

 and Wilsford (600 to 700 feet), the boundary of the flinty clay 

 being in some places not more than 20 feet above the outcrop of 

 the Chalk-Rock. Farther east, near Upavon, there are three small 

 patches below 600 feet ; but none has been mapped on Pewsey or 

 Milton Hills, although the latter rises to 782 feet above O.D. The 

 only other place within the area of Sheet 282 where Clay-with- 

 Flints has been mapped is on Sidbury Hill, where it flanks a small 

 outlier of Reading Beds at an elevation of about 700 feet. 



The southern portion of the area included in Sheet 282 and the 

 northern part of that which comes into Sheet 298 form together 

 the central portion of Salisbury Plain. All of this area lies below 

 600 feet, and is traversed by a network of branching-valleys. The 

 surface of what was originally a plain or plateau has evidently been 

 graded and lowered by long exposure to the action of rain, and the 

 ridges are capped by a variable thickness of flint-debris, consisting 

 partly of entire and unworn flints, and partly of broken angular 



