10 ON THE STRUCTURE AND MOTION OF GLACIERS 
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 6th of December, 1841, and published in the 
Edinburgh New Philosophical Journal for 1842.1. He was undoubtedly 
the first to give the phenomenon a theoretic significance. 
While engaged in the Lower Grindelwald glacier, we separated 
plates of ice perpendicular to the lamination of the glacier. The 
appearance presented on looking through 
Fig. 6. 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 elongated oval sections, re- 
sembling that of a double convex lens, and 
we therefore called this disposition of the 
veins “the lenticular structure.” In other 
cases, however, the sharpness of outline did 
not exist, but still the tendency to the 
lenticular form could be discerned, the veins in some cases terminating 
in washy streaks of blue. This structure is probably the same as that 
observed by Professor Forbes on the Glacier des Bossons, and 
described in the following words :—‘“ The veinsand bands .... . are 
not formed in this glacier by a simple alternation of parallel layers, 
but the icy bands have all the appearance of posterior infiltration, 
occasioned by fissures, thinning off both ways.” * 
In 1842 Professor Forbes undertook the survey and examination 
of the Mer de Glace, and finally arrived at a theory of glacier lamina- 
1 This communication gave rise to a discussion as to priority between Professor Forbes 
and M. Agassiz, for the details of which we must refer to the original papers on the subject. 
2 Travels, p. 181. 
