The ridge of the Lammermuir Hills in the south of Scotland, consists of
primary micaceous schistus, and extends from St. Abb's head westward, till it
joins the metalliferous mountains above the source of the Clyde. The
sea-coast affords a transverse section of this alpine tract at its eastern
extremity, and exhibits the change from the primary to the secondary strata,
both on the south and on the north. Dr. Hutton wished particularly to examine
the latter of these, and on this occasion Sir James Hall and I had the
pleasure to accompany him. We sailed in a boat from Dunglass, on a day when
the fineness of the weather permitted us to keep close to the foot of the
rocks which line the shore in that quarter, directing our course southwards,
in search of the termination of the secondary strata. We made a high rocky
point or headland, the Siccar, near which, from our observations on the
shore, we knew that the object we were in search of was likely to be
discovered. On landing at this point, we found that we actually trod on the
primeval rock, which forms alternately the base and the summit of the present
land. It is here a micaceous schistus, in beds nearly vertical, highly
indurated, and stretching from south-east to north-west. The surface of this
rock runs with a moderate ascent from the level of low-water, at which we
landed, nearly to that of high-water, where the schistus has a thin covering
of red horizontal sandstone laid over it; and this sandstone, at the distance
of a few yards farther back, rises into a very high perpendicular cliff.
Here, therefore, the immediate contact of the two rocks is not only visible,
but is curiously dissected and laid open by the action of waves. The rugged
tops of the schistus are seen penetrating into the horizontal beds of
sandstone, and the lowest of these last form a breccia containing fragments
of schistus, some round and others angular, united by an arenaceous cement.
Dr. Hutton was highly pleased with appearances that set in so clear a light
the different formations of the parts which compose the exterior crust of the
earth, and where all the circumstances were combined that could render the
observation satisfactory and precise. On us who saw these phenomena for the
first time, the impression made will not easily be forgotten. The palpable
evidence presented to us, of one of the most extraordinary and important
facts in the natural history of the earth, gave a reality and substance to
those theoretical speculations, which, however probable, had never till now
been directly authenticated by the testimony of the senses. We often said to
ourselves, What clearer evidence could we have had of the different formation
of these rocks, and of the long interval which separated their formation, had
we actually seen them emerging from the bosom the deep? We felt ourselves
necessarily carried back to the time when the schistus on which we stood was
yet at the bottom of the sea, and when the sandstone before us was only
beginning to be deposited in the shape of sand or mud, from the waters of a
superincumbent ocean. An epocha still more remote presented itself, when even
the most ancient of these rocks instead of standing upright in vertical beds,
lay in horizontal planes at the bottom of the sea, and was not yet disturbed
by that immeasurable force which has burst asunder the solid pavement of the
globe. Revolutions still more remote appeared in the distance of this
extraordinary perspective. The mind seemed to grow giddy by looking so far
into the abyss of time; and while we listened with earnestness and admiration
to the philosopher who was now unfolding to us the order and series of these
wonderful events, we became sensible how much farther reason may sometimes go
than imagination can venture to follow. As for the rest, we were truly
fortunate in the course we had pursued in this excursion; a great number of
other curious and important facts presented themselves, and we returned,
having collected, in one day, more ample materials for future speculation,
than have sometimes resulted from years of diligent and laborious research."

---John Playfair, 1788