Rev. Edwin JSill — Low-tide Causeways. 361 



all glacier beds known to me, nor are their contents in the least like 

 ice stones. Again, Duroclier long ago showed that the greater part of 

 the Drift of Scandinavia has not been derived from the Dovrefelds and 

 the higher lands between Norway and Sweden, or from Lapland, 

 but from the much lower grounds of Central Sweden. He says 

 distinctly that the mineralogical structure of the Scandinavian 

 blocks found in South Sweden and in North Germany shows that 

 they came from the low and mammillated hills of Sweden and 

 Finland, and not from the higher mountains. Those mountains ai-e 

 schistose, while the greater portion of the blocks are granitic, and 

 granite occurs in those mountains in only very small quantities. 

 (Bull Soo. Geol. France, 1846, pp. 64-5.) He thus objects 

 to the theory of Murchison and Verneuil that the erratics were 

 derived from the lands projecting above the ancient Northern Sea, 

 whose existence everyone admits, and that they were carried away 

 from them by icebergs, and thus floated over the water. This latter 

 view seems quite untenable iu the presence of the fact attested by 

 Durocher. 



{To he conduded in out next Number.) 



IV. — Low- TIDE Causeways. 

 By the Rev. Edwin Hill, F.G.S. 



I SUPPOSE that most of us are familiar with the processes by 

 which necks of land are cut down, by which promontories are 

 turned into peninsulas, and the peninsulas into islands, while the 

 islands in their turn become rocks. 1 have elsewhere called attention 

 to all stages of the jDrocess as shown in the four corners of Sark. On 

 the south there is the Coupee causeway, an isthmus 200 feet above 

 sea-level, with a crest only some six feet in width ; on the north, 

 an isthmus yet lower, and parts beyond already being separated by 

 the sea ; on the west, an island, Breqhou ; on the east, rocks, the 

 Burons. There are to be seen all stages of the process, but does 

 that process always proceed through all those stages to the end ? 



Many years ago, one in a party of frolicsome youths, I swam with 

 them to an islet in a lonely Scotch loch. We intended to explore 

 the unexplored, for there was no boat on the loch. We were, 

 however, rather disappointed by the discovery that this apparently 

 inaccessible islet was really joined to the land by a submerged ridge 

 scarce under water ; we need not have swum, for shallow wading 

 would have sufficed. Since then I have frequently noticed such 

 bars similarly joining rocks or islets to a neighbouring mainland ; 

 I have noticed them not only in such fresh- water lochs, but on the 

 coast of the sea as well. Such, for instance, are the connections, 

 passable at low tide, between the Jersey beach and Elizabeth Castle 

 in St. Aubin's Bay ; between Guernsey and Lihou, formerly also ihQ 

 access to Castle Cornet ; there are many others, less conspicuous, 

 in the Channel Islands. For all these, I think there is the same 

 natural origin. 



The cutting down of an isthmus is accomplished sometimes by 



