By William Gowland, F.S.A., F.LG. 



51 



and in the monoliths respectively, suggests considerations of very 

 great interest and importance, both to the archaeologist and the 

 geologist. » 



I. Sarsen Stones. — The nature and origin of these masses of 

 sandstone have been very fully discussed by Professor T. Kupert 

 Jones. 1 They are concreted portions of a Tertiary sandstone, either 

 of the Woolwich and Beading beds, as suggested by Sir Joseph 

 Prestwich, or of the Bagshot beds, as maintained by Mr. Whitaker. 

 All the usual characters of the different varieties of sarsen are 

 illustrated among the fragments collected at Stonehenge. With 

 the exception of casts of rootlets and stems, fossils are almost 

 entirely absent from these sarsens. Sir Joseph Prestwich found 

 in one of the monoliths of Stonehenge a layer of shells, 2 but I have 

 not detected any trace of shells in any of the fragments I have 

 examined, nor, so far as I am aware, have shells ever been found 

 in any of the sarsens lying on the surface of the downs. In their 

 microscopic characters, when studied in thin slices, 3 they show 

 great differences according to their composition and state of in- 

 duration. In some cases they are coarse-grained, in others very 

 fine-grained ; the sand grains of which they are composed are 

 sometimes well rounded, at other times angular. Other minerals 

 present in them besides quartz are felspars, more or less altered, 

 mica, and glauconite, while chips of flint are in some cases not rare. 

 The grains sometimes show only a small quantity of cement 

 between them ; at other times this siliceous cement is large in 

 quantity and the outlines of the original grains can be traced only 

 with difficulty, the rock being almost undistinguishable from a 

 quartzite. Occasionally the cement around the grains shows the 

 radiated or spherulitic appearance which is so well known in the 

 case of the Ightham stone described by Professor Bonney. 4 



1 "History of the Sarsens," by Professor T. Kupert Jones, Part I., Wilts 

 Arch. Mag., xxiii. (1886), 122-154 ; Part II., Geological Magazine, Dec. IV. 

 viii. (1901), 54-59 and 115-125. 



2 Prestwich, Geology of Oxford and the Thames Valley (1871), 447. 



3 " Note on the Structure of Sarsens," Geological Magazine, Dec. IV. viii. 



(1901), 1. 



4 Geological Magazine, Dec. IV. v. (1888), 299. 



E 2 



