STONEHENGE — STEVENS 453 



Avebury and Stonehenge called for exceptionally large stones of a 

 special shape, which would mean that they had to be sought out and 

 selected over a fairly wide area, and tliis applies particularly to the 

 "tabular" Sarsens, which most readily lent themselves to the pur- 

 pose of the Trilithons at Stonehenge. 



With the exception of the "Friar's Heel," all the Sarsens at Stone- 

 henge are tabular blocks. 



THE PRESCELLY STONES 



The Sarsens usually awake the greatest interest by reason of their 

 size and the difficulties presented by their erection to a primitive 

 race. 



But a far greater problem is presented by the Prescelly stones, 

 which, though smaller ii> size, have traveled to Wiltsliire from Pem- 

 brokeshire, a distance of 180 miles as the crow flies. 



For many years the place of origin of these stones was a matter of 

 controversy. One theory advanced was that they had been brought 

 to Salisbury Plain as boulders of "glacial drift." This has been 

 heavily discounted by the fact that no pebbles of that particular 

 stone appear in the local gravels. Others have sought their home in 

 Cumberland, Devonshire, and Cornwall. Finally, the late Dr. 

 Thomas proved beyond all question that their origin was in the hills 

 at Prescelly. 



Today 34 of these stones remain to us, and have been grouped as 

 follows : 



Dolerites 29 



Rhyolites 4 



Micaceous sandstone 1 ("Altar Stone") 



The dolerites are crystalline igneous rocks, of a blue-green to green- 

 ish-gray color, with white spots varying in size from that of a pea 

 to a walnut. This is a special characteristic of the Stonehenge 

 dolorites. 



The rhyoliteg are masses of volcanic rock (lava). 



The micaceous sandstone (Altar Stone) differs from the tM^o above- 

 named rocks and should be regarded as apart from them. Three 

 localities have been suggested, the Mendips, Glamorganshire, and 

 Pembrokeshire. The Altar Stone has special affinity to the last two 

 localities, which are more or less identical in structure, and it is almost 

 certain that South Wales is the locality from which this stone was 

 brought. If this is so it seems more probable that the stone came 

 from Milford Haven than from Glamorganshire. Both dolerites and 

 rhyolites are to be found in the Prescelly district and at no great dis- 

 tance from Milford Haven. The spotted dolerite of Prescelly has all 



