GLACIATION^ OF THE OEKNET ISLANDS. 657 



limestone, oolitic calcareous breccia, fossil wood (probably oolitic), 

 chalk, and chalk-flints, all of which are foreign to the island. When 

 we come to collate the evidence regarding the primary glaciation, 

 we shall discuss the probable localities from which these blocks 

 were derived. At present it is suiRcient to state that the evidence 

 is clearly in favour of their having been carried from the mainland 

 of Scotland. 



Equally important is the presence of numerous fragments of 

 marine shells throughout the deposit. Though we examined the 

 section with the utmost care, we did not succeed in dislodging a 

 complete shell ; indeed so worn are the fragments that it was with 

 the utmost difliculty that we obtained specimens sufficiently well 

 preserved for determination. !Nearly all the fragments are smoothed 

 and striated, like the stones in the Boulder-clay ; and there can be 

 little doubt that these characteristics are due to the very same cause 

 in both cases. Amongst the broken shells we detected fragments 

 of Cyprina islandica, Mytilus, and Mya truncata; but a careful 

 search, after severe storms, by some local collector would certainly 

 increase this list considerably. 



In the island of Shapinshay shelly Boulder-clay occurs at various 

 localities on the east coast, as at Kirkton, where it contains finely 

 striated chalk-stones. The best sections, however, occur along the 

 western shore, and especially in the bay south of Galtness, where it 

 forms a bluff cliff washed by high tides. This cliff furnishes valuable 

 evidence regarding the ice-carry, inasmuch as we noted amongst the 

 included stones blocks of the slaggy diabase which occurs wi situ in 

 the south-east corner of the island, along with striated fragments 

 of the sandstones which are associated with the volcanic rocks. In 

 this section smooth blocks of chalk and oolitic limestone, with 

 numerous fragments of marine shells, were also observed. 



If we traverse the Mainland from Scapa and Kirkwall westwards, 

 by the Loch of Stennis, to the crystalline axis north of Stromness, 

 similar conclusive evidence regarding the north-westerly movement 

 of the ice is obtained from the Boulder-clay. On referring to the 

 map of Orkney, it will be seen that the narrow zone of red and 

 yellow sandstones which crosses the Mainland from Inganess to 

 Scapa extends south-westwards along the shore as far as Orphir 

 Kirk. Now, in the shelly Boulder-clay in Kirkwall Bay, to the east 

 of the pier, striated blocks of red sandstone are commingled with the 

 flagstones in the clayey matrix. The latter are by far the most 

 numerous, and are likewise beautifully scratched along the major 

 axis ; but the sandstone blocks constitute a fair percentage of the 

 included stones. Prom the lithological character of these blocks, 

 we had no hesitation in concluding that they had been derived from 

 the sandstones to the east of Kirkwall. 



Again, in the sections occurring on the coast between Houton 

 Head and Irland Bay, the observer cannot fail to note the gradual 

 increase in the number of the sandstone blocks in this deposit as he 

 approaches Houton Head, a phenomenon which is quite intelligible 

 when he remembers that the striations along the shore point W. 

 Q. J. G. S. No. 144. 2 t 



