1816.] An Essay on Rents. 125 
and relative situation of such parts of the grained earth-stone, it 
becomes evident that they are the visible parts of a concentrie layer 
which underlies, but is united to, the compact layers. Let us in- 
stance the primitive district in Cornwall and Devonshire. If a 
person views the section of the largest granite hill near Redruth, 
taken in a straight line towards Dartmoor, in this direction the 
surface of the granite descends regularly till covered with the com- 
pact layer; then this layer descends also in the same direction, for 
a certain distance, but not so steep as the grained layer, or granite. 
Let this person now remove himself to Dartmoor, and take a sec- 
tional view of this hill in a straight line to the granitic hill near 
Redruth. The Dartmoor granite descends towards Redruth pre- 
cisely in the same way as the Redruth granite does to Dartmoor, 
till it is covered by the compact layer; which also declines to the 
place where it dips to from Redruth. Now the inference is, 
that these are two of the highest parts of a granitic layer which lies 
totally under the compact layer in this part of the country ; and the 
fact is, that the granite and granitic veins, which proceed from it, 
are found in the intermediate space between Redruth and Dartmoor. 
The same conclusions may be drawn if a person looks towards the 
granite near the Land’s End, or towards the Bristol or British 
Channels. Hence these granitic masses are but the visible parts of 
a grained layer that lies under the compact layer in this part of the 
world. Now as all granite or other grained parts present the same 
appearance as these, and exist in every elevated part of the earth- 
stone, the grained layer which is found in Cornwall is but a part of 
such a layer that continues in every direction round the world, and 
appears in every country, in consequence of having an undulating 
surface, whose eminences reach above the compact layer. Finally, 
specimens of the different varieties of grained earth-stone, such as 
granite and sienite, approach so near one another im appearance, 
that it requires the most expert mineralogist to determine with pre- 
cision to which variety some of them belong. There, therefore, 
appears to be no difficulty in the way in supposing that granite and 
sienite are portions of the same mass; on the contrary, this deduc- 
tion might have been drawn from their approximating appearances. 
The undulated surface of the earth-stone was produced in the 
following manner. ‘The process of consolidation proceeded upwards 
from below till it reached the earth’s surface. Before it had acted 
on the grained layer, a number of inequalities commenced in the 
surface, which divided the solid from the fluid matter, because the 
matter below contracted more, and in consequence sunk lower in 
one place than in another; as the consolidation continued upwards, 
these inequalities increased, and at the surface gave rise to the 
undulations which I have described, when speaking of the earth’s 
features, as being peculiar to primitive districts, and also produced 
such undulations as contain a series of stratified formations in their 
lower parts. ‘The hollow between the top of Keswick Mountains, 
6 ; 
