THE GEOLOGY OF ORKNEY. Ixxxi 
the base of the hills and forms a large part of the 
land surface of that country. 
It seems reasonable to believe that at one time 
Orkney was joined to Caithness and formed a 
northern extension of the Caithness plains. Dr 
Crampton’ has pointed out that the topography of 
Caithness and of Orkney have many points in com- 
mon. In Orkney the main ridges of high land lie on 
the west side, in Hoy, Orphir, Firth, and Harray, and 
this seems to be a continuation of the Dorrery Hills 
and the main watershed of Caithness that passes out 
to sea at Dunnet Head. In Orkney, as in the north- 
east of Scotland generally, the high ground lies to the 
west. The distance, for example, from the main 
watershed at Wideford Hill to the east side of 
Stronsay and Sanday is very great compared with 
that to Breckness and the western coast. At one 
time a great part of the North Sea must have been 
dry land, and the insignificant burns of the east of — 
Orkney flowed out across a plain now submerged, 
uniting gradually to form more and more important 
rivers, and ultimately mingling their waters with 
larger streams that gathered the drainage of the 
Rhine, the Elbe, and other rivers of north-western 
Europe. 
The land stood for a long time at this high 
level (probably several hundred feet higher than 
at present), and the water-courses were gradually 
deepened and widened till the main features of 
Orkney, as we see them now, were developed. 
There is a good deal of evidence to show that the 
1 The Geology of Caithness, Mem. Geol. Survey, 1914. 
