The Cruise of the Betsey: or, A Summer Ramble Among the Fossiliferous Deposits of the Hebrides. With Rambles of a Geologist or, Ten Thousand Miles Over the Fossiliferous Deposits of ScotlandMiller, Hugh
Philosophy
The Cruise of the Betsey: or, A Summer Ramble Among the Fossiliferous Deposits of the Hebrides. With Rambles of a Geologist or, Ten Thousand Miles Over the Fossiliferous Deposits of Scotland
Miller, Hugh
Geology -- Scotland
I was accordingly introduced to Mr. Bremner, and passed, in his company
the half-hour which we spent in the bay, in a way that made me wish the
time doubled. I had been struck by the peculiar style of masonry
employed in the harbor of Wick, and by its rock-like strength. The gray
ponderous stones of the flagstone series of which it is built, instead
of being placed on their flatter beds, like common ashlar in a building,
or horizontal strata in a quarry, are raised on end, like staves in a
pail or barrel, so that at some little distance the work looks as if
formed of upright piles or beams jambed fast together. I had learned
that Mr. Bremner had been the builder, and adverted to the peculiarity
of his style of building. "You have given a vertical tilt to your
strata," I said: "most men would have preferred the horizontal position.
It used to be regarded as one of the standing rules of my old
profession, that the 'broad bed of a stone' is the best, and should be
always laid 'below.'" "A good rule for the land," replied Mr. Bremner,
"but no good rule for the sea. The greatest blunders are almost always
perpetrated through the misapplication of good rules. On a coast like
ours, where boulders of a ton weight are rolled about with every storm
like pebbles, these stones, if placed on what a workman would term their
best beds, would be scattered along the shore like sea-wrack, by the
gales of a single winter. In setting aside the prejudice," continued Mr.
Bremner, "that what is indisputably the best bed for a stone on dry land
is also the best bed in the water on an exposed coast, I reasoned
thus:--The surf that dashes along the beach in times of tempest, and
that forms the enemy with which I have to contend, is not simply water,
with an onward impetus communicated to it by the wind and tide, and a
reactive impetus in the opposite direction,--the effect of the backward
rebound, and of its own weight, when raised by these propelling forces
above its average level of surface. True, it is all this; but it is also
something more. As its white breadth of foam indicates, it is a subtile
mixture of water and _air_, with a powerful _upward_ action,--a
consequence of the air struggling to effect its escape; and this upward
action must be taken into account in our calculations, as certainly as
the other and more generally recognized actions. In striking against a
piece of building, this subtile mixture dashes through the interstices
into the interior of the masonry, and, filling up all its cavities, has
by its upward action, a tendency to _set the work afloat_. And the
broader the beds of the stones, of course the more extensive are the
surfaces which it has to act upon. One of these flat flags, ten feet by
four, and a foot in thickness, would present to this upheaving force, if
placed on end, a superficies of but _four_ square feet; whereas, if
placed on its broader base, it would present to it a superficies of
_forty_ square feet.
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