and Motion of Glaciers. 373 



Geological Society of France assembled at Porentruy in September 

 1838j M. Guyot gave the following interesting description of the 

 phsenomenou: — "Since the word layer has escaped me, I cannot 

 help recording as a subject of investigation for future observers a 

 fact, regarding which I dare not hazard an explanation; especially 

 as I have not encountered it more than once. It was at the summit 

 of the Gries, at a height of about 7500 feet, a little below the line 

 of the first or high 7ieve, where the ice passes into a state of gi-a- 

 nular snow In ascending to the origin of this latter (the gla- 

 cier of Bettelmatten), for the purpose of examining the formation 

 and direction of the great transverse fissures, I saw under my 

 feet the surface of the glacier entirely covered with regular fur- 

 rows from 1 to 2 inches in width, hollowed in a half-snowy 

 mass, and separated by protruding plates of an ice more hard 

 and transparent. It was evident that the mass of the glacier 

 was here composed of two sorts of ice, one that of the furrows, 

 still snowy and more easily melted, the other that of the plates, 

 more perfect, crystalline, glassy and resistant; and that it was 

 to the unequal resistance which they presented to the action 

 of the atmosphere that was due the hollowing of the furrows, 

 and the protrusion of the harder plates. After having followed 

 them for several hundred yards, I reached the edge of a great 

 fissure, 20 or 30 feet wide; which cutting the plates and furrows 

 perpendicularly to their direction, and exposing the interior of 

 the glacier to a depth of 30 or 40 feet, permitted the structure 

 to be observed on a beautiful transverse section. As far down 

 as my vision could reach I saw the mass of the glacier composed 

 of a multitude of layers of snowy ice, each two separated by one 

 of the plates of ice of which I have spoken, and forming a whole 

 regularly laminated in the manner of certain calcareous slates." 



A description of this structure, as observed upon the glacier of 

 the Aar, was communicated by Professor Forbes to the Royal 

 Society of Edinburgh on the Gth of December 1841, and pub- 

 lished in the Edinburgh New Philosophical Journal for 1842*. 

 He was undoubtedly the first to give the phfeuomenon a theo- 

 retic significance. 



While engaged in the Lower Grindelwald glacier, we sepa- 

 rated plates of ice perpendicular to the lamination of the gla- 

 cier. The appearance presented on looking through them, was 

 that sketched in fig. 6. The layers of transparent ice seemed 

 imbedded in a general milky mass; through the former the light 

 reached the eyes, while it was intercepted by the latter. Some of 

 the transparent portions were sharply defined, and exhibited elon- 

 gated oval sections, resembling that of a double convex lens, and 



* This communication gave rise to a discussion as to priority between 

 Professor Forbes and M. Agassiz, for tlie details of which we must refer to 

 the original pajpers on the subject. 



