ANCIENT GLACIERS IX EASTERN HEMISPHERE. 167 



developed terminal moraine extends in a great sweep 

 so as to obstruct the drainage and convert thousands 

 of acres of land into lake and morass, which is only now 

 yielding to artificial drainage. Many fine examples of 

 drumlin and esker mounds occur at low levels in differ- 

 ent parts of the island ; and it was remarked nearly fifty 

 years ago by dimming, that their long axes were parallel 

 to the direction of ice-movement indicated by the striated 

 surfaces and the transport of boulders. 



"The foreign boulders are mainly from the granite 

 mountains of Galloway, but there are many flints, pre- 

 sumably from Antrim, a very small number of Lake Dis- 

 trict rocks, and a remarkable rock containing the excess- 

 ively rare variety of hornblende, Riebeckite. This has 

 now been identified with a rock on Ailsa Crag, a tiny 

 islet in the Frith of Clyde ; and a Manx geologist, the 

 Rev. S. N. Harrison, has discovered a single boulder of 

 the highly characteristic pitchstone of Corriegills, in the 

 Isle of Arran. 



" The So-called Great Submergence. 



" It may be convenient to adduce some additional facts 

 which render the theory of a great submergence of the 

 country south of the Cheviots untenable. 



" The sole evidence upon which it rests is the occur- 

 rence of shells, mostly in an extremely fragmentary condi- 

 tion, in deposits occurring at various levels up to about 

 1,400 feet above sea-level: A little space may profitably 

 be devoted to a criticism of this evidence. 



" Mod Tryfaen (' The Hill of the Three Rocks ').— This 

 celebrated locality is on the first rise of the ground between 

 the Menai Straits and the congeries of hills constituting 

 ' Snowdonia ' ; and when we look to the northward from 

 the top of the hill (1,350 feet) we see the ground rising 

 from the straits in a series of gentle undulations whose 

 smooth contours would be found from a walk across the 



