Professor T. Rupert Jones — History of Sarsens. 55 



bound together by a flinty substance, as in the exposed blocks o{ 

 Eocene sandstone known as ' Grey-weathers ' in Wiltshire, and 

 which occurs also [Landenian, sandstone] over the north of Franca 

 towards the Ardennes" ('-Textbook," 2nd ed., 1885, p. 162). 



In a letter, Sir Archibald has obligingly stated that the first and 

 best account on which the reference to the above was b ised is by 

 Dr. C. Barrois, Ann. Soc. Geol. du Nord, vol. vi (1878-9), p. 8GG. 

 See also his short paper in the Assoc. Fran^aise, 1879, p. 6G6, 

 Gosselet quotes Barrois in his gi'eat work " L'Ardenne," 1888, p. 829. 

 Further references are also given by these two authors. 



188o. The Rev. A. Irving, taking it for granted that a large river 

 in Eocene times flowed from a region of Palceozoic rocks in the west, 

 in the direction of the Thames Valley to the east, said that the detritus 

 would be quartzose and feli^pathic ; the felspars would ultimately be 

 decomposed by the agency of carbonic acid, and gehitinous liyilnted 

 silica would be produced. (Proc. Geol. Assoc, vol. viii, pp. 150, 157.) 



1887. The Rev. A. Irving, in a letter dated March 6th, LS87, 

 writes : — " You have overlooked one point which I have tried to bring 

 out in some relief — the fact that the surface acquires a poicelhiuous 

 texture, not duo to cementation by iron (for from the sup^rtioial 

 layer tlie iron is entirely leached out), but to an actual change of the 

 material by a solution-process. I suggesteil (three or four years 

 ago) C 0^ as the chief assent ; but later work has shown me that the 

 organic acids contained in pea It/ water have played a far more 

 potent part in this sub-metamorphic change." 



1888. In the Geological Magazine, Dec. Ill, Vol. V, 

 Dr. T. G. Bonney states that the Sarsens of the Tertiaries are of 

 concretionary origin : " In the Sarsen Stones, and with matrix of 

 the Hertfordshire Pud<1ingstones, tliei e is chalcedonic silica converting 

 sandstone into quartzite" (pp. 298-300). 



1888. J. Prestwich: "Geology," etc., vol. ix, p. 342. "These 

 sands [of the Woolwich and Reading Series] also occasionally 

 contain concreted blocks in irregular local beds of sandstone, 

 sometimes with very liard siliceous cement." Footnote at p 342 : 

 " Mr. Whitaker and Prof. Rupert Jones think that in Berkshire and 

 Wiltshire they [the Sarsens] are more frequently derived fiom the 

 Bagshot Sands." The ' Puildingstone ' of Bucks and Herts is here 

 referred to the Reading Be<ls. Further on, at p. 3G4, it is stated 

 that Sarsens occur in the Bagshot Sands of Frimle}' and Chobham. 



N.B. — Concretionary action has produced in many Sarsens 

 mammillations on a large scale, which show on some surfaces 

 irregular, coalescent, smooth swellings, with shallow, valley-liUo 

 slofjcs and depressions, like those on the so-called ' bowel-stones ' 

 of the Lower Greensand near Aylesbury. H. B. Woodward's 

 "Geology of England and Wales," 2nd ed. (1887), p. 377. Such 

 mammillated Sarsens occur in Suffolk, Wiltshire, and elsewhere. 



N.B. — The convexity of the lower face of a Sarsen l}'ing in its 

 original sand-bed is due to the concretionary formation of tiie stone. 



1901. J. W. Judd's "Note on the Structure of Sarsens" 

 (Gkol. Mag., January, 1901, pp. 1, 2) gives definite descriptions 



