162 LARGE BOULDER FOUND AT BRANKSOME. 



running water which deposited this gravel was not capable 

 of transporting this block, weighing half a ton. Is there 

 any agent other than ice capable of having done this work, 

 and is the presence of the boulder evidence of a glaciation 

 of Dorset ? We may at once dismiss an explanation some- 

 what recklessly advanced, namely, that the stone was buried 

 by human agency. The soil above it was evidently undis- 

 turbed and has never been cultivated, and to suppose that 

 anyone would dig a hole 8ft. deep to bury a stone beneath 

 Ashley Road is absurd. But we may ask, is it not possible 

 that the stone lay on the top of the Bagshot sands, and was 

 there buried beneath the Plateau gravel ? I have not been 

 able to ascertain the depth of the gravel at this point, or 

 whether any exists under as well as over where the boulder 

 lay. This question could easily have been answered at the 

 time of the excavation ; but inquiries made of the workmen 

 later elicited no trustworthy information. All we can now 

 do is to ascertain the nature of the stone itself. Is it a 

 sarsen, or greywether, similar to the other sarsens derived 

 from Tertiary rocks and widely scattered over the Downs of 

 Wilts and Dorset, or is there no source in the neighbourhood 

 from which it can have been derived, so that it must have 

 been brought from further afield, and may fairly claim the 

 title of an erratic ? These questions are not easy to answer. 

 Sections of the stone have been prepared for microscopic 

 examination by Dr. H. Colley March, who has also had 

 slides made, for purposes of comparison, from a typical 

 sarsen lying in the Valley of Stones, near Bridehead.* They 



* Photographs of these slides, enlarged 22 diameters, have been kindly 

 made by Dr. Flett, and are here reproduced. An interesting feature in the 

 Branksome slide is that the rock contains many small grains of brown 

 tourmaline, some of which are large enough to be seen with a pocket lens. 



1. Bridehead sarsen, photo with crossed Nicols. 



2. Same, in ordinary light. 



3. Branksome boulder, photo with crossed Nicols. 



4. Same, in ordinary light. 



