60 Recent Excavations at Stonehenge. 
they were found would have so greatly diminished their weight 
and the difficulties of their transport? The same people, as we 
have seen, in dealing with the blocks of sarsen-stone (which were 
probably moved only a few hundreds of yards) would appear to 
have left only the final dressing to be done after their transport, and 
to have reduced their weight as far as possible before removal. 
I have long believed that the explanation of the true source of 
these “foreign rocks” is to be found in the circumstance that such 
materials are constantly found transported as boulders of the 
glacial-drift. It is true that the “southern limit of the boulder 
clay” is usually placed by geologists considerably to the north of 
Wiltshire; but it is a well-known fact that scattered boulders 
often occur far to the south of this limit. The sheets of boulder 
clay which now cover so large a part of the country are merely 
relics of an originally much more widely spread formation. 
In many places the boulder clay has been greatly diminished in 
thickness by denudation,and deep valleys have been cut through itby 
the existing rivers. Many tracts where the boulder clay was thin 
have probably been swept quite bare of the formation, except for 
the large boulders that would be left behind. A proof of this is 
found in the fact that the gravels of the rivers of the South of 
England, including those which drain Salisbury Plain, contain 
many fragments of “foreign rocks” which must have been derived 
from the boulder clay, and among these it would not be difficult to 
select representatives of the “bluestones” and fragments from the 
soil of Stonehenge. I have myself seen a boulder of a slaty rock, 
comparable in size to the largest of the “ bluestones ” of Stonehenge, 
on the hills to the south of London. 
It may doubtless be objected that such large boulders of foreign 
rock do not now occur anywhere upon Salisbury Plain. But it 
must be pointed out that rocks of considerable hardness and 
durability are everywhere sought for and utilised for millstones, 
gate-posts, and for road-metal. Even the widely distributed sarsen- 
stones are rapidly disappearing, the blocks, especially the harder ; 
ones, being broken up and carried away for building-stones and 
_ road-metal; and it is certain that the much more sparsely distributed 

eee ee 
