GLACIATION or THE OEKI^EY ISLANDS. 653 



regarding the direction of the ice -movement ; for in Odin Bay, 

 where an important section of Boulder-clay occurs, which we shall 

 describe presently, the striae point W. 15°-35° N. ; between Kirk- 

 buster and Einga the trend is W. 10°-40° N., at Burgh Head 

 W. 40° N., and north of Holland W. 40° ]N". On the western coast- 

 line, on the shores of Eousholm Bay, the direction varies from 

 W. 41° ]S[. to N. 40° W. ; and on the shores of Linga Sound it is 

 W. 40° N. It is of the utmost importance to note the perfect 

 agreement in the trend of the ice-markings in different parts of this 

 island, because it indicates a persistent movement in one determinate 

 direction. 



A careful examination of the striated surfaces on Shapinshay 

 confirms in a remarkable manner the evidence regarding the ice- 

 flow during the primary glaciation in the northern islands. Along 

 the west coast, between Galtness and Stromberryness, the direction 

 varies from W. to N.W., while on the shores of Yeantro Bay, which 

 indents the northern part of the island, the markings point N.W. 

 and N. 35°-40° W. Further along the eastern coast-line, between 

 Gioness and the school-house, the direction is W. 30° JST., and the 

 same trend is observable southwards towards the church ; near 

 Poot striae were noted pointing N. 30° W., and close to Haco's Ness 

 N.20°W. 



It is impossible, within the limits of this paper, to describe the 

 various instances we met with in the Mainland, and we will there- 

 fore merely indicate the general trend in different parts of the 

 island. On the glaciated surfaces of granite and gneiss north of 

 Stromness numerous examples occur trending W. 15°-20° N. and 

 W. 12° S. Immediately behind the town the direction varies from 

 W. 8°-40° N., while on the moorland between Yesnabae and the 

 Loch of Stennis, as well as at the Eing of Brogar, the same varia- 

 tion is observable from W. 12° N. to N.W. 



On the hill-slopes overlooking Gorsness and the island of Gairsa 

 the average direction of several examples is JN". 25°-30° W., and 

 along the coast-line from Irland Bay to Houton Head the trend 

 varies from W. 12°-42° N. One instance occurs in Irland Bay 

 pointing W. 32° S., which probably belongs to the later glaciation. 



In KirkwaU Bay, a short distance to the east of the pier, 

 beautifully striated flagstones may be seen where Boulder-clay has 

 been recently removed by the action of the sea, the striae running 

 JS". 6° W. and InT.N.W. ; and so also on the surfaces of the flagstones 

 in the Scapa Quarry the direction is N". 8°'W. Along the shore 

 from Scapa to Howquoy Head the average direction of several 

 examples is 'N. 30°-35° W., and near St. Mary's the trend varies 

 from N.W. to K. 25° W. 



In the southern islands striae are not so abundantly found, owing 

 to the readiness with which the soft yellow sandstones and marls 

 crumble away when long exposed to the denuding agencies. In 

 South Ronaldshay several examples occur, the general direction of 

 which is W. 20° N. These may be seen on the cKff-tops near 

 Stow Head and Halcro Head by removing the coating of Boulder- 



