_ terwards to disappear, 
| The Glacial Theory of Prof. Agassiz. 355 
while small stones often sink into cavities, large ones seem hoisted on 
pedestals. Masses of all kinds tend towards the sides of the om 
and many of these huge blocks are found scattered along the flanks of 
the Alpine valleys, some having remained there, stranded as it were. 
Others are found in the middle, far from existing ice, and were proba- 
bly left there when the glacier disappeared. _We have thus an expla- 
nation of the erratic blocks so common in this country, when’these do 
not come from very distant stations. Being stranded by their greater 
weight, while the smaller matter moved onward, or left sticking om the 
soil in consequence of the final fusion of the ice, we can understand why 
they are often found perched on the sides of steep declivities. 
_ Blocs perchés, so named for the reason just given, are sometimes 
found; in very singular situations. 
Let a, figure 6, be the surface of the glacier, r the top of a pines 
ing rock in situ. The ice has the block } floating on it; it encom- 
passes the fixed rock nearly on a level with its summit, and in travelling 
downward strands the block upon it. The block may be stranded on 
the very summit, as C. ree Fig. 6. as 9 Ak 2 
Supposing the glacier af- peri care 7 
here we would have an_ 
angular block perched on (== 
an isolated hill, or as Agas- 
siz terms it, a pyramid, ; a 
with a steep declivity below ie sank we ‘woukd be puzzled to conceive 
7 what agent it was planted in so singular a situation. 
Figure 7 represents erratic blocks in a different situation, but quite 
as singular. 7 is a projecting fixed rock, rising considerably above the 
glacier aa; the reflection of the sun’s heat from its surface melts a 
portion of the ice, and forms a cup-shaped cavity round it. Into this 
cavity blocks of various sizes fall by their weight from the surface of 
the ice as, it glides onward, and settle on the flanks of the hillock. Sup- 
posing the glacier to disappear, this conical rock would have a ring of 
Stones like a coronet encircling its summit, and we would be apt to 
wonder at the mysterious agency which brought them there, and left 
the lower parts of the hill destitute of them: Agassiz names various 
—— rocks amidst the Alpine glaciers with such circles of stones 
round them, or with single blocks stuck upon them, as in figure 6. 
The same phenomena oe on Mount Jura, where no glaciers now 
exist. 
~ Creux and Lapiaz.—On the sides of the Swiss valleys, round holes! 
such as cascades make, are sometimes found in the rock ; but in places 
remote from running waters, and where the form of the surface wil 
