OF MARLBOROUGH. XXI 



of it hardened blocks of sandstone were found, some of 

 which have been removed and others left undisturbed. 

 The pit runs down by the side of a heavy, dark-red clay, 

 containing large flint-nodules, which bulges out beyond the 

 perpendicular on the north side of the pit and then recedes 

 again, the sand running in under the clay at the bottom. 

 This sand probably formed part of the Plastic Clay series, 

 which at one time covered this district, and of which there 

 are still some remains in the south-eastern part of the Forest. 

 After the greater part of the sand had been eroded, there 

 seems to have been a peak of sandstone left here, which 

 resisted denudation, and round which the boulder- clay was 

 deposited. The hardened blocks of sandstone, which are 

 similar to the boulders met with in almost every valley 

 or depression of the surface t>f the clay or chalk, as well as 

 in the clay, bear out Mr. Prestwich's theory as to the for- 

 mation of the boulders that they are hardened portions of 

 the sands of the Plastic Clay or Woolwich and Reading 

 series ; but their position on and in the Drift-clay, even to 

 the depth of 10 and 12 feet below the surface, shows that 

 they must have been removed from their original positions 

 by the same causes which deposited the Drift-clay. These 

 boulders occur on the tops of the Chalk hills, but in great 

 abundance in the valleys, especially at Lockeridge, and in 

 Clatford Bottom to the north of the Bath Road, where they 

 are heaped upon one another in a most promiscuous manner, 

 as if they had been dropped by icebergs. Many of these \ 

 boulders are of large size, weighing as much as 90 or 100 ) 

 tons ; and some of the largest were chosen by the Ancient' 

 Britons to form their temple at Avebury. 



An outlier of the Lower Bagshot Clays and Sands is met 

 with at the Obelisk, in Savernake Forest. The clays are 

 used for making bricks. 



The beds consist of undulating layers of 



(i) Olive-green sandy clay (partly denuded), 



