Sir Henry Howorth in his Ice or Water deals in considerable detail with the various theories of glacier motion which have been propounded. His works are veritable mines of information concerning the subject of ice and water, and he is everywhere anxious to give all workers credit for the work they have done, to state their theories correctly, and if he should differ from their conclusions to do so in a kindly spirit. Among other theories of glacier motion he refers to the one for which I am responsible. Referring to this theory he says—

“In the Philosophical Magazine for 1888 Mr. Deeley propounded what he claimed to be a new theory of glacier motion. In this paper he very rightly says ‘that every change of outline suffered by a glacier, if we disregard melting and the small internal changes of bulk produced by pressure, etc., is due to the shear of ice plane over ice plane’. He further says of glacier motion: ‘We have, therefore, two kinds of motion—one a bodily slide in a downward direction, and another due to the differential motion of the ice not in contact with the ground.’ In order to explain the latter he postulates that constant liquefaction and resolidification is taking place within a glacier by the sun’s heat penetrating it and melting certain portions, and inasmuch as a glacier has a tendency to sink in consequence of its gravity, the liquefying of certain portions of its interior will take away the support of the rest and let it sink down.