The walls of rock on either side are very sheer, and increase of course in height as the plane of entrance falls.

The whole length of the slope is about 420 feet, and down a considerable part of this some grasses and flowers are to be found: the last 208 feet are covered more or less with ice; though, at the time of my visit, the furious rains of the end of June, 1864, had washed down a considerable amount of mud, and so covered some of the ice.

There were no ready means of determining the thickness of this layer of ice, for the descent of which ten or eleven zigzags had been made by the farmer.

In one place, within 24 feet of its upper commencement, it was from 2-1/2 to 3 feet thick; but the prominence of that part seemed to mark it out as of more than the average thickness.
Even where to all appearance there was nothing but mud and earth, an unexpected fall or two showed that all was ice below.

Whether the driver had previously experienced the treacherousness of this slope of ice, or whatever his motive might be, he left me to enter and explore alone.
The roof of the entrance is at first a mere shell, formed by the thin crust of rock on which the surface-earth and trees rest high overhead; but this rapidly becomes thicker, as shown in the section of the cave, and thus a sort of outer cave is formed, the real portal of the glaciere being reached about 60 feet above the bottom of the slope.