274 A Geological Sketch of the Valley of the Kennet. 



of the London basin, genera are found from the top to the bottom 

 of the formation, which will only exist in shallow water ; ^ whilst 

 in others the foraminifera, embedded in the various strata, indicate 

 an uniform sea depth of about 100 fathoms,- leading to the con- 

 clusion that the accumulation of sediment, and a depression of the 

 ocean bed, went on at the same time gradually and uniformly ; and 

 that they were so equal in amount as to neutralize each other, and 

 cause no change in the conditions of animal life. 



Immediately above the London Clay, there lies a formation 

 designated the Bagshot beds, on account of its extensive develope- 

 ment in the neighbourhood of Bagshot Heath. It consists of fine 

 sands of various colours, and layers of clay. Where it exists in its 

 original bulk it is upwards of 500 feet in depth ; but in this neigh- 

 bourhood the greater part of it has been swept awaj% and only thin 

 layers and outliers of it are found. No one need lament its absence, 

 for it is generally the most sterile and uninteresting of all the 

 tertiary beds. It occupies most of the commons in the neighbour- 

 hood of Newbury, and good sections of it may be seen on Bucklebury, 

 Woodhay and Inkpen Commons, Fossils are of rare occurence in 

 it in this vicinity ; but some have been found near Newbury, which 

 show that here as well as in some other places, the formation, though 

 for the most part of marine origin, is not entirely so. Not far from 

 the Union "Workhouse, a bed of white pipe-clay was exposed some 

 years since, at a depth of 30 feet from the surface, in which were 

 leaves of plants identical with vegetable remains discovered in the 

 freshwater strata, belonging to the lower Bagshot beds, in the Isle 

 of Purbeck, and the Isle of Wight. It has been conjectured that 

 the sarsen stones and grey wethers, which are scattered over many of 

 our chalk downs, and which lie in prodigious numbers on the country 

 west of Marlborough, are remains of Bagshot beds, which at one 

 time rested on the chalk, and which some tremendous inundation 

 of the sea swept away, leaving those ponderous ruins of the form- 

 ation behind it.^ 



'Journal of the Geological Society, vol. iii., p. 374. 

 ^ Memoirs of Geol. Survey, No. 7, p. 46. 

 ' Mr. Prestwich, who has carefully investigated the origin of the sarsen stones, 

 thinks that they have been derived chiefly from the Woolwich and Eeadiag 



