
































By William Gowland, F.S.A., FIC. 51 
and in the monoliths respectively, suggests considerations of very © 
great interest and importance, both to the archeologist and the 
geologist. 
I. Sarsen Stones.—The nature and origin of these masses of 
sandstone have been very fully discussed by Professor T. Rupert 
Jones.!_ They are concreted portions of a Tertiary sandstone, either 
of the Woolwich and Reading 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,? 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,*? 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 
ntity and the outlines of the original grains can be traced only 
ith difficulty, the rock being almost undistinguishable from a 
quartzite. Occasionally the cement around the grains shows the 
adiated or spherulitic appearance which is so well known in the 
se of the Ightham stone described by Professor Bonney.* 

‘History of the Sarsens,” by Professor T. Rupert Jones, Part I., Wilts 
h. Mag., xxiii. (1886), 122-154; Part II., Geological Magazine, Dec. IV. 
ii. (1901), 54-59 and 115-125. 
_ 2 Prestwich, Geology of Oxford and the Thames Valley (1871), 447. 
* “Note on the Structure of Sarsens,” Geological Magazine, Dec. IV. viii. 
(1901), 1. 
4 Geological Magazine, Dec. IV. v. (1888), 299. 
E 2 
