440 MR. D. PIDGEON ON CEETAIN PECFLIAEITIES OF 



rolling, and why are none of them bored or encrusted by Annelidan 

 tubes? 3. Why, on the other hand, do certsim fragments of lime- 

 stone pebbles Trhich have been riddled by borers occur in the 

 deposit? 4. "Why do Annelidan incrustations occur only on the 

 pebbly stones in the deposit, and how have such incrustations 

 escaped destruction from beach-rolling ? 5. How, the bulk of its 

 stony component being local in character, were the few small foreign 

 stones in it brought into the deposit ? 6. Why is there no indica- 

 tion of stratification in these raised beaches * ? 



Again, as to the shelly components of these beaches : — 



7. Why does Jialf the deposit consist of shells, while these (except 

 in the case of beaches composed entirely of shells and their frag- 

 ments, not in question here) form such an insignificant proportion 

 of existing beaches ? 8. Why are the shells for the most part 

 broken, and why do their fragments preserve sharp edges? 9. 

 Why are there so few beach-rolled shells or shell -fragments in the 

 deposit ? 10. Why are none of the unbroken, and scarcely any of 

 the broken shells either incrusted by Annelidan tubes or perforated 

 by marine borers? 11. Why are all the Eivalves broken? 12. 

 Why has the group of shells (see Mr. Hunt's list referred to above) 

 a somewhat northern aspect ? 



The answers to these questions must, in the author's opinion, be 

 sought in the study of certain Arctic phenomena, to which the 

 attention of geologists was first drawn by Feilden and De Ranee. 

 They say f " there is no point of greater interest in Arctic geology 

 than the occurrence of water-margins at successive elevations in 

 Smith Sound, rising to heights of from 200 to 300 feet, in situations 

 where wave-action was impossible. These ancient sea-margins are 

 most persistent in bays, inlets, and narrow arms of the sea ; and 

 are still in process of formation." 



During the short Arctic summer, upon the first signs of thaw, 

 masses of rubbish fall from the cliffs and form immense screes, 

 which not only reach, and cover, the " ice-foot," but are often carried, 

 in part, by the impetus of their fall, on to the floes beyond it. 

 Towards the close of the thaw episode, the sun's rays, being rapidly 

 absorbed by the dark surface of the " screes," melt the uppermost 

 layers of the ice-foot at its point of contact with the hill-side, thus 

 producing a deep trench, filled, as soon as it is formed, by water 

 which, at this season of the year, pours from the uplands. 



The overflow from the trench in question, escaping over the ice- 

 foot, cuts deep channels within a few hours across the latter, 

 draining the ditch at low-tide, while at high-tide the sea pours 

 through these transverse gullies into the trench and, sweeping right 

 and left, with more or less violence, assorts and reasserts the stony 

 chips which it contains. 



Meanwhile, the waves throw all sorts of "jetsam" both upon- the 

 surface of the ice-foot and into the ditch, mingling shells, weed, 



* There is none seen in the lumps of beach exhibited, 

 t Quart. Journ. Geol. See. vol. xxxviii. p. 563 (1878). 



