TRANSACTIONS OF THE SECTIONS. 59 



of the glacier; and as, in all the upper regions at least, the icy mass progresses from nar- 

 rower to broader valleys, every movement has the effect of leaving a narrow space 

 between the margin of the glacier and its containing walls. The granular snow which 

 covers the flanks of the valleys, being loosened and softened during the heat of the 

 day, slips down and fills these spaces, when the descent of the temperature during 

 the night, and the contact with the already formed icy mass consolidates it into a layer 

 of solid ice. Layers of ice in this position are recognized to be always more or less 

 granular, but to be divided from each other by plates of purer and more compact ice. 

 Dr. Stark regarded these plates as a superadded structure, occasioned by the trickling 

 of the water of the melted ice or snow over the external surface of each layer where 

 they were in contact, or nearly so, with the containing rocky walls. The water 

 would freeze as it trickled over the icy surface, and form a plate of pure and trans- 

 parent ice very different from the recognized structure of ice formed from granular 

 snow. From these longitudinal and vertical layers varying in thickness from a frac- 

 tion of an inch to several inches, Dr. Stark regarded their formation as a matter of 

 daily occurrence, the thicker layers being either produced by the spaces not having 

 been filled up for several days, or from the glacier having advanced more one day 

 than it did another. 



3. On the Combination of Horizontal with Longitudinal and Vertical Strata. — It was 

 remarked that in this combination the- horizontal layers would always be found to 

 occupy the middle of the glacier, whilst the longitudinal and vertical strata would 

 compose its breadth. No writer known to Dr. Stark described such a combination 

 of strata as occurring in any glacier $ but it was mentioned that a careful examina- 

 tion of the recorded observations of different authors who described the same glacier, 

 showed that such a combination must exist. Dr. Stark stated that the only possible 

 mode of explaining the apparently discordant statements of authors relative to the 

 position of the strata in glaciers, was to suppose that as the mass composed of hori- 

 zontal strata advanced onwards, it received in the manner above indicated a lateral 

 increase of longitudinal and vertical strata, which, at the same time they increased 

 its breadth, probably also added to its depth, by running for a greater or lesser ex- 

 tent below the already formed icy mass. It was shown that so long as the glacier re- 

 mained in the upper regions, it probably received additional horizontal layers from 

 the snows of each year or each storm, which would cover both the already formed 

 horizontal and longitudinal layers. When the glacier however descended so far as 

 to waste away from its upper surface, the horizontal layers from lying uppermost, 

 would first disappear, so that by the time it arrived at the level of the first line or so, 

 only a narrow band of horizontal layers might occupy the middle of the glacier, or 

 the whole might have completely disappeared, leaving the longitudinal alone appa- 

 rent. The ascertained difference of depth between the glacier in the upper and 

 lower valleys seemed of itself to prove, in Dr. Stark's opinion, that such must be the 

 way in which the horizontal layers disappeared, as all agree in stating that the 

 depth of the icy mass in the upper valleys is three or four times greater than in the 

 lower ones; and as none allow that in these elevated situations they melt away 

 from their lower surface, they must become thinner by wasting away at their upper 

 surface. 



4. On the Appearance of Longitudinal and Vertical Stratification in Layers depo- 

 sited horizontally. 



5. On the Occurrence and Mode of Formation of Transverse more or less inclined 

 Strata. — As the most remarkable and best-known point where this peculiar structure 

 exists, and where it is seen forming, Dr. Stark instanced the terminal portion of the 

 Rhone glacier, after it falls into the valley of the Rhone over the rocky barrier or 

 precipice which separates that valley from the Gallenstock. He stated, that at the 

 central point on which the icy cataract falls no structure was visible, but that at some 

 distance from this an appearance of layers running transversely began to be mani- 

 fested, and that a series of transverse layers could be traced from this spot to the 

 very termination of the glacier, each layer lying at a lesser angle or dip as that 

 termination was approached. The lowest or terminal layer was mentioned to lie 

 at an angle or dip of from 10° to 15°, whilst every layer above that lay at a 

 higher and higher angle, rising even to an angle of 70°, as the central heap was 

 approached. 



