The Theory of Glacier motion. 115 



Glaciers," dated July the 4th, 1842 {s^e Ed. New Phil. Jour., 

 XXXII., p. 338 — 341), and they were amply confirmed 

 in later experiments (id.^ 341 — 345), from which it more 

 clearly appeared that the motion was not the same from 

 day to day and week to week. He also shewed that 

 this variation is common to all parts of the glacier, 

 whether compact or fissured, and that the dispropor- 

 tion in the movement of the centre and sides of a 

 glacier is greatest in the lower and faster moving part 

 of it, where it varies from one-third to one-half of the 

 smaller velocity, and least near the origin of the glacier, 

 where it is only one-quarter or one-fifth. The similar 

 variation also affects the centre more than the sides. The 

 greatest daily motion he measured was 27* i inches. 



The veined structure in ice was apparently first described 

 by M. Guyot, in 1838, on the Glacier of Gries. He noticed 

 below, under his feet, he says, furrows an inch or an inch- 

 and-a-half wide, separated by ridges of harder and more 

 transparent ice ; the ice consisted clearly of two kinds, one 

 white and melting early, the other more perfect, crystalline, 

 and hard. Their unequal swelling caused the furrows. On 

 looking down a crevasse, which cut the furrows at right 

 angles and shewed a transverse section of 30 to 40 feet, the 

 ice seemed everywhere composed of layers of white opaque 

 and transparent ice, as regularly stratified as certain cal- 

 careous rocks, (see Huber, des Glacier, p. 107, quoted by 

 Moseley, Phil. Mag., 4th Sen, XXXIX, 241 ). Forbes described 

 this structure, which he independently discovered, as the 

 ribboned structure of ice. 



The general course of the bands, as pictured on the 

 surface of the glacier, is a succession of oval waves passing 

 into hyperbolas with the greater axis directed along the 

 glacier. The actual shape of the curves depends very much 

 on the configuration of the glacier. In narrow canal-shaped 

 glaciers, the lines are nearly parallel and vertical, inclining 



