26 
PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
immediate proximity to it, the ring that it gives to the 
stroke of the hammer, all tell the same tale. If we now 
descend to the bed of the river, we see that the trap-dyke 
crosses the stream almost in a line with the bridge, and 
that the deep pool which we noticed from above has been 
formed by the same causes and in the same manner as the 
one which we first examined. 
Continuing our walk down the riverside for about half- 
a-mile, we find another remarkable trap formation occur¬ 
ring at the dam-dyke above Cromwell Park Works. The 
trap rises sheer from the river, and a very fine section is 
laid bare on both sides. Columnar formation is here dis. 
tinctly perceptible. The columns are of course arranged 
horizontally, or at right angles to the cooling surface. The 
dyke is about the same breadth as the one which we saw 
at Dalcrue, and presents even more distinct marks of its 
igneous origin and molten state. The rock which it 
pierces is a soft marl, and the hardness of the rock in con¬ 
tact with the trap presents a marked contrast to its soft 
condition a few feet distant. On looking at the bed of the 
river here, we see neither trap-dyke nor deep pool below 
the line in which the dyke must run. There was a deep 
pool at this spot, but it has been filled up to allow the 
dam to be constructed. Prom what we now see, we may 
learn the value, in a practical point of view, of a little 
acquaintance with Nature’s mode of working. Where the 
pool has been filled up the channel of the river is floored 
with large stones, carefully dressed and laid. This floor¬ 
ing was at first placed with the stones sloping downwards 
with the current. The result of laying them down in this 
position was that the first big spates wrenched them out 
and swept them away. Taking a lesson now from the 
manner in which Nature slopes the stones in the bed of a 
stream, the builders replaced the pavement, making the 
stones slope in the opposite direction. The result of fol¬ 
lowing Nature’s plan has been that the biggest floods roll 
over the stone flooring without inflicting damage. The 
materials for filling up the pool were quarried out of the 
trap-dyke by the riverside. An enterprising individual, 
on seeing the hard and strang6 character of the rock in 
the immediate vicinity of the trap, imagined that he had 
discovered a stone which would do admirably for road 
metal. A quantity was quarried and duly broken. Un¬ 
fortunately for the success of the experiment, the indurated 
marl, on being broken into fragments and exposed to the 
action of air, rain, and frost, speedily resolved itself into its 
original state of mud. These two facts, which I have from 
undoubted authority, show the advantage in practical 
matters of some knowledge of Nature and her mode of 
operation. 
Resuming our walk, a few steps bring us to another 
dyke. I shall detain you here only a moment, in order to 
show that the stream has at this spot washed away the 
dyke itself, and has left the indurated sandstone which 
was in contact with it to form the sides of a narrow deep 
pool, which bears the appropriate name of “The Black 
East.” 
It would give me pleasure to take you further down the 
river, and point out to you the high cliffs of red sandstone 
rising on both sides; but the limits which have been most 
judiciously prescribed to papers read before this Society 
are now almost reached. At the bridge at Almondbank, 
another notable trap-dyke appears crossing the river. 
The features with which we are now familiar are here also 
presented to us. I pass them over. An easy and pleasant 
walk from Perth will take you to the spot, and the scene 
will amply repay the trouble. 
We have thus in less than two miles passed five trap- 
dykes, and we may see—1. That they all run in the same 
direction. 2. They are of more recent origin than the 
sandstone which they have penetrated. 3. The piercing 
of the sandstones by the trap has not in general altered 
their dip at the point of contact. The first dyke, however, 
which we visited shows an alteration of the dip of the 
sandstone at the point where the river first impinges upon 
the trap. 4. Though the igneous action which sent up 
these dykes has ceased, the process which has hollowed 
out the pools, and cut the rocks, and formed the steep and 
precipitous cliffs, is still in operation. Old men tell us 
that they can discover little or no change that has been 
wrought in their day, but the threescore years and ten are 
only as a moment compared with the vast epochs neces¬ 
sary to produce the results which have been disclosed to 
ns in the scenes which we have now traversed. 
2, “ Some Suggestions anent Specimens for the Museum .” 
By Dr Buchanan White, F.L.S. 
. Though in several of his addresses our President has, 
in his usual lucid manner, given a description of the plan 
on which our Museum is to be arranged, and has pointed 
out in what manner members may assist in procuring 
specimens of the natural productions of Perthshire, it has 
occurred to me that a few more words may not be amiss at 
the present time, when we are just on the eve of entering 
into possession of our new building. As most of you are 
aware, one of the objects of the Society is the acquisition 
of a collection—as perfect as it is possible to make it—of 
all the animals, plants, and rocks of Perthshire, with the 
view not only of thereby showing in the most evident 
manner (i.e., by the specimens themselves) what these are. 
