266 A. J. JuJces-Broicne—T/ie Formation of ' Till.' 



Even if geologists will give up asking for a tilt of the axis, and 

 be content with a new shape, still the mathematician asks whether 

 they have realized the Earth's size. ' Its deviation from a sphere is 

 trifling in amount.' In what amount ? In figure doubtless. Were 

 its section drawn on this page a microscope would be wanted to 

 distinguish the curve from a circle. But in quantity the deviation is 

 not trifling. The height of the highest mountain and the depth of 

 the deepest sea together do not equal its extent. All the mountain 

 chains added together would not perceptibly increase the volume of 

 the equatorial protuberance. The mass of all the continents re- 

 inforced by that of all the seas would not be the fifth part of it. 

 To change the Earth's shape this vast protuberance must be shifted 

 or masked. "Where is the power that can shift it, the elevation that 

 can mask it? What are our puny upheavals and subsidences of an 

 ocean here and a continent there compared with a girdle of matter 

 thirteen miles in thickness? Take an extreme supposition. Eemove 

 10,000 feet of rock from the surface of one-half the Earth and 

 spread it over the other half. You could not thereby bring the pole 

 half way to the present Arctic circle. Sufficient changes in the 

 Earth's surface will undoubtedl}' shift the pole. But will geologists 

 grant the changes that would be sufficient ? 



IV. — The Formation or Till. 

 By A. J. Jukes-Browne, B.A., F.G.S. 

 OTWITHSTANDING the numerous papers which have lately 

 JLM been written on the subject of glacial deposits, there is one 

 question of fact which does not appear to have been satisfactorily de- 

 cided. I refer to the formation of Till underneath glaciers, concern- 

 ing the possibility of which somewhat different statements were put 

 forward by two writers in the February Number of the Geological 

 Magazine. 



The following passage occurs in Dr. James Geikie's paper on the 

 Preservation of Deposits under Till : — " It is needless to refer one to 

 the petty glaciers of the Alps and Norway to prove that glacier-ice 

 cannot both erode its bed and accumulate debris upon that bed at one 



and the same time No considerable deposit could possibly 



gather below alpine glaciers like those of Switzerland and Norway ; 

 but underneath glaciers of the kind that invaded the low grounds 

 of Piedmont and Lombardy we know that thick deposits of tough 

 Boulder-clay, crammed with scratched stones, did accumulate," 



At a later page of the same Number Mr. G. Linnarsson animad- 

 verts upon a portion of Prof. Milne's " Travelling Notes," which have 

 recently appeared in this Magazine, and says — "That, actually. Till 



this diameter will have turned with the Earth's diurnal motion so as to lie in the 

 same line but reversed. The rotation produced at the former line will be in the 

 opposite direction to that now being caused, and will be neutralized by it. The 

 afternoon will undo the morning's work. This explanation is very insufficient, giving 

 no account of Precession, but it may assist those unacquainted Avith Rigid Dynamics 

 in comprehending how the Sun may be perpetually di-awmg the Earth's equator 

 towards coincidence with the Ecliptic, yet never bringing it any nearer. 



