not enable it to pass through a tortuous valley. The diameter of the great basin of the Glacier de Talèfre, on the range of Mont Blanc, is six times as great as the outlet through which the frozen stream eventually squeezes itself. Saussure's explanation throws no light upon this point, and it is quite plain that the philosopher had failed to hit upon the true theory of glacier motion.
We will pass over the theory of M. Agassiz, which was founded on a radical error, and proceed to consider that advanced by Professor James Forbes of Edinburgh. In 1842, this celebrated geologist undertook an extensive series of observations; from which dates the commencement of all sound and accurate knowledge respecting our moving lands. The laws of glacier motion were established by a few simple observations. He showed that the glacier moves onward with such regularity that it is almost possible to tell the hour by the progress of a point placed on the surface; but that the motion is less rapid in summer than in winter, in damp than in dry weather, at night than during the day. The different parts of the same glacier do not advance at a uniform rate, and the centre invariably moves more rapidly than the sides. If a series of points be laid out in a straight line across the glacier, they will be rapidly bent into the form of a regular curve, by the gradual decrease of velocity from the centre to the sides. Further observations in subsequent seasons proved that the upper part of the glacier moves faster than that near to the bottom.
