By Mr. Cmmington, P.G.S. 145 



dense felsite with the gmall regular white specks, one of green 

 diabase, and one of the soft schist. 



The concrete-like substance in which the base of the obelisk is im- 

 bedded has apparently been produced by ramming into the hollow 

 round the stone when it was erected, a quantity of soft chalk, mixed 

 very freely with small flints (chalk and flint constitute the natural 

 subsoil of Stonehenge), and with numerous fragments of all the 

 different kinds of stone of which the building is composed. By the 

 subsequent infiltration of rain-water, chemical compounds have been 

 introduced, which have filled up the interstices, solidifying the whole 

 in the course of ages, into the tough concrete-like mass found round 

 the foot of the obelisk. 



This concreted mass contains, irregularly distributed throughout 

 it, certain compounds beside the carbonate of lime (the chalk), of 

 which it mainly consists. " These compounds, though not separable, 

 in a complete and unchanged condition, betray their presence by 

 physical characters, and by the occurrence in the concrete, of alumina 

 and ferric oxide as bases, and by silica and organic acids. Probably 

 rain and other meteoric water charged with oxygen and with carbonic 

 acid (and also with organic acids from the turf and roots) have 

 effected such changes in the silicious rocks and chalk as may now 

 be observed to occur in many chalk-pits wJiere coUyrite and allophane 

 are still being formed." ^ 



The following are the rocks found in the concreted mass^ 



' Professor Church has kindly undei-taken the chemical examination of this 

 part of the suhject. The result of his qualitative analysis is expressed in the 

 above paragraph, but he hopes some time this year, when his Roj^al Academy 

 lectures are over, to push on the enquiry, and to furnish a report to the next 

 number of the Wiltshire Magazine. 



