GLACIA.TION OF THE OEKNEY ISLANDS. 659 



east of Hoy hill a moraine mound, nearly half a mile long and 

 from fifty to sixty feet high, runs across the mouth of the glen. 

 It would seem that the later glacier which filled the valley did not 

 succeed in scooping out the moraine profonde belonging to the 

 primary glaciation, as the moraine matter rests on stiff" sandy 

 Boulder- clay. Purther, in the hollow below Coulax hill several 

 concentric heaps were observed which extend across the valley, 

 indicating pauses in the retreat of the glacier. 



In the Mainland also the moory ground between Finstown and 

 Maes Howe is dotted all over with conical moraine heaps, evidently 

 deposited by the glaciers which moved off' the northern slopes of the 

 Orphir hills. On the east side of the range of hills that runs 

 north from Pinstown several parallel moraine ridges may be ob- 

 served not far from Ellibister. Again, in the peninsular tract to 

 the south-east of Kirkwall, a splendid series occurs in a valley 

 situated about three miles north of Graemshall. At the point where 

 the highroad from Roseness joins that from St. Mary's to Kirkwall, 

 the concentric arrangement of the moraine heaps is admirably 

 displayed. 



YI. Eekatics. 



Boulders do not occur very plentifully in Orkney ; but we felt 

 convinced, from an examination of those we met with, that they 

 must have been mainly distributed during the primary glaciation. 

 In Westra blocks of granite and quartzite are found on the slopes 

 of Cleat hill ; and rounded stones and boulders of red sand- 

 stone from Eda occur in the southern district as well as along the 

 western shores. 



In the north of Sanda, at Saville, a remarkable boulder of gneiss 

 is met with, which has been described by previous observers. It 

 measures Q^ x 'o X 2\ feet above ground, but its base is buried 

 underneath the surface. Professor Heddle, who has made a minute 

 examination of this boulder, states that it does not appear to be a 

 British rock. He gives the following description of it in a recent 

 number of the ' Mineralogical Journal'*: — " It consists in greatest 

 amount of white finely striated oligoclase, the crystals of which are 

 penetrated by fine filaments of actinolite, glassy quartz in much 

 smaller amount, dark green finely foliated lustrous hornblende in 

 well-marked crystals, very little of a pale-green mica, a minute 

 amount of a pale-brown mineral, which may, but does not ap- 

 pear to be sphene, and a speck or two apparently of thorite. The 

 mass also contains a single crystal of pale-green apatite four or five 

 inches in length by over an inch in width, and this apatite con- 

 tains imbedded cryptolite." 



He states that the only Scotch rock resembling the Saville 

 boulder which he is aware of is to be found in Sutherlandshire ; but 

 it has orthoclase as its felspar, and does not contain apatite. Should 

 this boulder really prove to be of Scandinavian origin, its presence 



*■ Mineralog. Journal, vol. iii. p. 174. 



