202 GREYWETHERS AT GRAYS THURROCK, ESSEX. 



hard Tertiary stones. Mr. Whitaker [Geol. London, etc.^ pp. 478- 

 80) has some remarks on " Greywethers and Pudding Stones," 

 in which he discusses the distribution and probable origin of 

 both. He agrees with Professor Prestwich in thinking that 

 they have been largely derived from the Woolwich and Reading 

 Beds ; though at the western end of the London Basin, where 

 they are most numerous, *' the origin of the greywethers may be 

 traced to the Bagshot Sands." At Grays it seems most probable 

 that the greywethers have been derived from the \yoolwich and 

 Reading Beds, which occupy a considerable area at the surface 

 between Stanford-le-Hope and Wennington, and were once 

 continuous with the beds of the same age on the Kentish shore 

 opposite. Between Orsett and Stifford, and thence towards- 

 Avele}', they occupy much less of the surface than between 

 Orsett and Stanford-le-Hope. But this results mainly from the 

 fact that from Orsett westward their outcrop is much more 

 largely hidden by the Old Thames river deposits than fromi 

 Orsett eastward. And in these old river deposits, formed 

 when the Thames was flowing about 100 feet above its 

 present level, the Grays greywethers were seen. 



It is curious to note in the section at Grays showing these 

 greywethers in place, the absence of any signs of disturbance 

 caused by the entrance of these weighty masses of stone into- 

 the fine gravel and sand. During the gradual changes in the 

 position of the channel of the old Thames these blocks seem to 

 have been deposited in it most gently and gradually, having 

 travelled but a few yards from the place at which they were 

 originally formed. A stream bringing down to a certain part of 

 its course, in time of flood, a debris of tree trunks with other 

 organic remains mixed with gravel and sand would show a much 

 more disorderly channel section in later times, from the perishable 

 nature of much of the material, than would be afforded by 

 the gradual letting-down of some weighty but almost indes- 

 tructible greywethers in the same place. 



