DAVIS : EREATIC BOULDERS. 
269 
the parts marked E, El, E2, and is almost entirely made up of 
Mountain Limestone. Towards the S.E. it terminates in a bold 
escarpment which is continued westwards and overlooks Clapdale. 
This plateau constitutes a base from which rises other escarped 
beds of limestone to the height, at F, of about 1300 feet above 
the sea level. 
The whole of the surface of the limestone plateau between 
A, E, and F, is thickly strewn with masses of Silurian Grit, some 
of these are of immense size, and weigh many tons, Blocks 16 
to 20 feet in diameter are not uncommon, some are so perched 
on the underlying limestone as to form rocking stones. These 
masses of rock are generally quite angular in form, and do not ex- 
hibit any scratches or marks of giaciation ; they are frequently 
split and broken in various directions by subaarial agencies. In 
numerous instances the grits have served as a protection to the 
limestone beneath them, and they are now supported on limestone 
pedestals 18 to 24 inches in height. This circumstance leads 
naturally to the inference that, since the period during' which the 
Silurian rocks were carried and deposited where they are now 
found, the surface of the limestone has been lowered, except 
where protected by the overlying masses of Silurian rocks, to the 
extent of nearly two feet ; and considering that this large amount 
of denudation is entirely due to the subaarial agencies of rain, frost, 
and wind — whose action is very slow — there must ha\e been a 
lapse of time of great length since the Erratics were carried to 
their present resting place. 
The boulders are ranged in three directions or streams. The 
principal one extending from A to E, and El has been derived in 
a great measure from the thick bedded grits exposed in situ at A. 
The latter position is 900 feet above the sea level ; the ground 
rises to El, where the abrupt escarpment ending the plateau is 
1050 feet in height. Immense masses of the rock are laid 
immediately in front of the parent ridge at a much lower level, 
and the direction and progress of the glacier which tore them away 
and carried them forward is clearly shewn by the great blocks 
