Hon. Mr. Strangways on the Rapids of [matra. 341 
The surface of this platform is apparently now about fifty feet 
above the level of the water, at the lower extremity of the rapids. 
Its surface is in many parts quite bare, and deeply channelled in a 
direction parallel to the river. It is covered with heaps of pebbles 
and boulders of great size, some of which are hollowed and scooped 
into the most fanciful shapes. This sort of pierres fgurees is 
also found, but much smaller, below the falls. 
One of the largest of the blocks now left dry, marked in the plan 
and section, (Plate XVIII, letter F,) standing nearly in the middle 
of the elevated platform, is worn through perpendicularly with a 
cylindrical hole. Cases of a similar nature occur in the horizontal 
beds of chalk on the shore of the coast of Antrim ; in the bed of 
the TafF in Glamorganshire ; and near the rapids of precipitous 
rivers in all countries ; indicating the long continued action of a tide 
or rapid current rolling on its own axis a loose hard stone, which 
has got embayed so as to impede progressive, and allow only of 
a rotatory motion.* 
The rock is a slaty form of the common red granite of Finland, 
but contains more mica which lies in black plates between the 
laminae. This sort of granite is very easily disintegrated, and is 
found every where falling into gravel from the mere action of the 
weather. The laminae of the slate are nearly vertical, but what 
inclination they have is from west to east. 
* Cavities thns formed have been designated by the appellation of Rock Basins, a 
term which is also applied to the irregular pits and cavities often found on the surface of 
crags and blocks of granite and coarse sandstone, and which are referable t© the action of 
the atmosphere and rain upon the irregularly decomposing surface of the rock. Good 
examples of granite thus acted on may be seen on most of the granite hills of Cornwall, 
particularly at Cairn Brae, near Camborne, and in the neighbourhood of the Peak in 
Derbyshire ^ similar appearances occur on the summits of blocks of mill-stone grit. 
