GLACIATION OF THE OEKNEY ISLANDS. 655 



the southern districts. At Eackwik, near Stangar Head, it consists 

 of a tough tenacious gritty clay, which is chiefly made up of red 

 sandstone fragments, about 80 per cent, of the larger blocks being 

 composed of sandstones which are foreign to the island. Some of 

 these blocks, which are finely smoothed and striated, measure six 

 feet across. The deposit rests on the grey flagstones, and some 

 small subangular fragments derived from the underlying rocks are 

 likewise included ; but the great majority of the stones consist of 

 sandstones which we identified as belonging to the island of Eda. 

 Crossing the peninsula to the shores of Tuquoy Bay, similar sections 

 are presented, resting on grey flagstones, the included blocks being 

 composed of the underlying rocks, red sandstones, quartzites, and 

 chalk-flints. It is important to note that the red sandstone blocks 

 do not form such a large percentage at this locality, but that they 

 gradually diminish in number as we recede towards the north-west. 

 On the slopes of Cleat hill fragments of granite, quartzite, diorite, 

 and dolerite are associated with the flagstones in this deposit ; while 

 still further north, near the church, blocks of red and white honey- 

 combed sandstone and small pink granite stones were observed in 

 the Boulder-clay in addition to the local rocks. 



Along the west coast hardly any Boulder-clay is to be met with ; 

 but some thin patches are to be seen on the cliffs at Nonp Head, 

 containing well-striated stones derived from the flagstones of the 

 island. Occasional smooth blocks of Red Sandstone occur in the 

 hollows amongst the debris of the underlying rocks, which are, in 

 all likelihood, the relics of the once existing Boulder-clay. 



Now it is evident, on a moment's consideration, that the gradual 

 decrease in number of the red sandstones in the Boulder-clay, as 

 we traverse the island from the south-eastern headlands towards 

 the west coast, indicates that the ice-flow must have been towards 

 the Atlantic ; and when we consider that these sandstones nowhere 

 occur in situ in Westra, and that they could only have been 

 derived from the adjacent islands of Eda and Sanda, we are forced 

 to conclude that the ice-movement must have been altogether inde- 

 pendent of the islands. 



Along the east coast of Eda the Boulder-clay is not so abundant as 

 in some of the more sheltered bays on the opposite side of the island, 

 which is satisfactorily accounted for by supposing that the rocky 

 slopes facing Eda Sound were exposed to the full sweep of the mer 

 de glace. Here and there, however, patches do occur, as on the 

 north shore of Lonton Bay, where the deposit contains smoothed 

 and striated chalk-stones, along with blocks of red and white sand- 

 stones and grey flagstones. Its most noteworthy feature is the 

 presence of worn fragments of marine shells, which are scattered 

 irregularly through the stony clay. Similar sections occur in the 

 bay of Calf Sound near the pier, and also along the west coast near 

 the Wart of Eda, where shell-fragments were likewise observed. 



Perhaps the finest section of this deposit in Eda occurs along the 

 banks of a small stream which flows into the bay about a mile east 

 of Eara's Ness on the west coast. The stream has cut down through 



