1ft 8 Proceedings of the Royal Society 
“ Rocks of Sanda are wholly secondary strata, — sandstones, 
sandstone flag, breccia, and limestone. 
“ The only primary rocks in Orkney are in the largest islands 
(Mainland or Pomona), close by sea- port of Stromness, above 
30 miles distant from Sanda. Hill at back of Stromness seems 
granite, with outer coating of gneiss. The gneiss, which is 
similar in quality to the Sanda Moorstone, is traversed by 
dykes or veins of granite. 
“ About a mile to N.E. of Stromness secondary strata begin. 
From thence to Sanda only sandstone and limestone visible. 
“From Stromness to Burness Church is at least 34 miles in 
a direct line. 
“ On supposition that this gneiss tumbler in Sanda formed 
part of Stromness hill, it must have passed over 15 miles of 
what is land, and 19 miles of what is sea, at present. 
“The firths of Westra and Eda, between Stromness and 
Sanda, are of immense depth, * through which the waters of 
the Atlantic now rush with indescribable force towards east 
or German Ocean, at the ebbing of the tides/’ 
Dr Neill adds that he cannot imagine how this boulder 
transported from Stromness to Sanda, except by “what Saus- 
sure has termed a debacle,” “ the rush of vast torrents,” which, 
besides transporting the boulder, might “have also scooped 
out those hollows which are now the firths of Westra and Eda.” 
Stromness bears from Saville about W.S.W., and a straight 
line between the two places crosses not only several firths, but 
several islands. If the boulder came from Stromness, as sup- 
posed by Dr Neill, its transportation by land ice is inconceiv- 
able. 
Statistical Account states that granite rock, passing into 
gneiss, runs through Stromness parish, forming a tract about 
a mile wide, and six miles long (vol. xv. p. 46) ; and that all 
the rest of Orkney Islands are sandstones of different kinds. 
It is added, that “rolled blocks of granite are found in these 
islands far from their original position” (page 210). 
Whilst it is very probable that this Sanda boulder came, as 
* Admiralty charts show depths of water in these firths to he from 10 to 20 
fathoms. 
