9 6 



any foreign stones occurring here or in other patches of gravel 

 should not have been transported by floating ice to the district 

 where they were subsequently laid down in beds or patches. To 

 these causes we may attribute the occurrence of such specimens as 

 Dr. Colley March has exhibited, provided their ice-workmanship be 

 admitted. Specimens of these are shown in Plate IV. 



We next turn to the Sarsen stones, and enquire whether they 

 afford any evidence of ice-action. The origin of Sarsen stones is 

 well known geologically. They are fragments of quartz sandstone 

 and quartzite conglomerate, of various degrees of hardness and 

 size, composed of grains varying in size from a fine sand to a pea- 

 stone, cemented by silica or sometimes with traces of iron oxide.* 

 Sheets of similar material occur in occasional layers in Tertiary 

 strata, but chiefly in the Bagshot sands between the beds of clay, 

 sand and gravel. The formation of Sarsen stones can be examined 

 in situ near the bottom of Durley Chine, where a flat mass of 

 quartzite sandstone is now breaking up into fragments as the under- 

 lying clay and sand is washed away. In districts whence the 

 Tertiary strata have been denuded, after washing away the softer 

 beds, these flat masses of hard stone remained on the surface, being 

 quickly broken up into boulders of various sizes, partly by gravity 

 from their own weight — they being seldom more than one to two 

 feet in thickness — and also by the action of frost. Such stones 

 remain dotted over many Dorsetshire hills and heaths, where they 

 are known as "grey wethers." In cultivated lands they have long 

 been removed and broken up. Most of the stone circles and 

 dolmens in Dorset, as well as part of Stonehenge, are built of these 

 stones, which were far commoner in prehistoric times than now, and 

 were found ready to hand by Celtic and pre-Celtic workmen. Some 

 of these stones, by the well-known tendency of large boulders to 

 "creep," have found their way down hillsides to valley bottoms and 

 stream beds, Examples of the latter may be found at Wimborne 

 at the bridge near the centre of the town, others are found by the 

 stream at Nunney Castle, near Frome, whilst a curiously shaped 

 one was recently found by Mr. Chambers, of Pokesdown, in a 

 similar situation. In all these places Tertiary beds have been 

 denuded, and there seems no need to call in other causes to account 

 for the source and presence of Sarsens. These statements are 

 confirmed by the writings of Mr. Clement Reid, Mr. Whitaker, and 

 also Mr. Monkton, though the latter says that he has never seen 

 them as originally found in Bagshot strata.! I should like him to 

 examine the section referred to in Durley Chine. They are always 

 more or less water worn when found in valleys, and those on hill- 

 sides have been affected by the usual sub-aerial denuding forces. 



Lastly, Sarsens are occasionally found embedded in plateau 

 gravel. A notable instance of this is the stone discovered last 

 summer in Upper Parkstone, of which some photographs I took 



* Sarsens sometimes occur of a conglomerate nature, containing large flints, 

 usually sub-angular, as about Portesham and in the Valley of Stones, in Dorset. 



f- See paper on "Gravels of the Bagshot District," in Q.J.G. Soc, liv., and the 

 discussion following. 



