G. W. Buhnan — Formation of the Boulder-clay. 305 



Dec. 6. 9h. 55m., Invergarry, like a heavy carriage passing. 

 Dec. 26, Ih. 20m., Loch-hourn Head, a very slight noise and 



trembling of the floor on which the observer was 



standing. 

 Dec. 28. 20h. 20m. and 21h. 24m., Invergarry, like a heavy carriage 



passing. 

 Dec. 30. 9h. 45m., Invergarry, like a heavy train crossing a bridge. 



Doubtful Earthquake. 



The following shock is entered under this heading, having been 

 noticed by only one observer; but, judging from the careful descrip- 

 tion, I believe there can be little doubt as to its seismic nature. 



October 25, 1891, about 16/*., Bournemouth. — A notice of this shock 

 by Mr. Henry Cecil appeared in Nature (vol. 44, p. 614), and this, 

 together with a more detailed description which Mr. Cecil kindly 

 sent me, is the source of the following account. A dull thud was 

 heard, as of a heavy fall underground, and instantly afterwards (all 

 but simultaneously with it) a single momentary shock without any 

 preceding or following tremor. The observer's eyes were directed 

 at the time on a plant resting on the table beside him, and, when 

 the shock occurred, the long, pendant, lightly-poised leaves of the 

 plant were violently agitated, waving up and down through a large 

 arc for several seconds. The movement of the ground must have 

 been vertical, and Mr. Cecil remarks that his impression was that 

 it was first upward and then downward. It being Sunday afternoon, 

 almost all tralBc was suspended, but, shortly after the shock, a 

 heavy carriage passed along the adjoining road without producing 

 any perceptible movement in the plant. Mr. Cecil informs me that 

 he has felt several slight shocks at Bournemouth, and he believes 

 that in the present case the sound and shock were of seismic origin. 



IV. — AVas the Boulder-clay formed Beneath the Ice ? 



By G. W. BuLMAN, M.A., B.Sc. ; 

 Cor bridge - on- Tyne. 



GEOLOGICAL opinion is still divided on the subject of the 

 formation of the Boulder-clay. By some it is held to be the 

 sole work of the ice, and accumulated beneath it ; by others it is 

 looked upon as a marine deposit, though deriving its materials from 

 the grinding action of the ice-sheet or glacier. Some geologists, 

 again, hold that the "Till" — as distinct from the Boulder-clay — 

 was formed beneath the ice, but that the latter is a marine deposit 

 laid down in glacial seas. 



Neither the first nor the third of these views can as yet be said to 

 have received the stamp of geological certaintj^ for it has not been 

 conclusively shown that any such deposit is being formed beneath 

 the ice at the present day ; nor can it be inferred from what we 

 know of the properties of ice in the form of glacier or ice-sheet that 

 such a deposit ought to be the result of its action. 



Thus no deposit analogous to Boulder-clay is found in Switzerland 



DECADE HI. — YOL. IX. NO. VII. 20 



