on Strathearn. 363 
either escaped their notice, or appeared so mysterious and in- 
scrutable as to preclude all research. 
The human mind cannot now form any conception of that 
aspect which the’ surface of the earth originally had assumed, 
though it cannot be doubted, that from the various agents em- 
ployed in the mighty operations of Nature, exerted in giving 
form and stability to our planet, considerable irregularity must 
all along have diversified it; but those immense masses, which 
constitute what are called the primary mountains, seem in a great 
measure to have remained unaltered during the subsequent con~ 
-vulsions that produced the secondary structure, and gave to the 
universal body its present unequal appearance:—but a smooth 
and uninterrupted surface was incompatible with those laws which 
are supposed to have been cailed into action in the formation of 
the earth; and though it is not necessary, on the present occasion, 
to enter into the merits of the contending Volcanic and Neptunian 
theories, we must still be conscious that many series of facts con- 
stantly presented to our view on the exterior, as well as those 
that have been explored in the bowels of the earth, are consist- 
ent with, and may very plausibly be attributed to, the influence 
of both powers. 
For the purpose of exhibiting an object of geology more im- 
mediately within the reach of our own observation, we shall con- 
fine our remarks to an extraordinary change to which the beau- 
tiful and fertile valley of Strathearn has anciently been subjected ; 
and which, though perhaps of less importance to the naturalist 
than the prodigious altitudes and extensive dales of the Alps and 
Andes, are still worthy of admiration, as this tract possesses a 
variety of subjects interesting to the student of nature, and to 
the lover of her sublime and picturesque beauties. 
The great chain of the Grampian mountains, which consti- 
tutes the northern, as the Ochil hills do the southern, boundary 
of this valley, are in many parts composed of primitive matter 5 
but in several places this formation is surmounted by secondary 
rock of various character and diversity of alternation and position, 
The portion of those mountains in the vicinity of Lochearn, and 
what forms the immediate limitsof that lake, is not wholly granitic, 
their exterior being covered with wacke, different species of 
schistus, lime, and sandstone. Some beds of trap are also visible 
in its usual linear direction, traversing these rocks without regard 
to their stratification, and always dispesed in vertical walls. 
But the most striking features in the district of Strathearn are, 
the surprising changes that the ground has undergone by the 
different courses which the river has taken at various periods. 
These alterations are very evident in travelling along this exten- 
sive tract, from the departure of the river out of its parent lake 
to 
