The six remaining strata are all similar to each other, Consisting
of tabular basalt, but differing in thickness; and being separated only
by thin ochreous layers, the division is not always discernible.
From a revision of the various circumstances observable in these strata, Dr. Richardson selects certain facts which he considers of im- portance to geology. First, that every stratum preserves the same thickness throughout its whole extent. Secondly, that this uni- formity of thickness is interrupted only where the upper surface has been exposed by removal of the superior strata. 'l‘hirdly, that the curvature of the summits of the facades does not correSpond in form to the surfaces of the strata underneath. Fourthly, that the same arrangement does not continue for more than two or three miles. Fifthly, that wherever materials of different species are in contact, the line of demarcation is always distinct and well defined. Sixthly, that the upper part of any facades, where the strata are ex- posed, is generally perpendicular, and the lower steep and precipitous. Seventhly, that the rude masses which appear in the sea at the base of the precipices, are not, as has been supposed, ruins which have fallen from the strata above, but are remnants of lower strata remaining in their original position. Eightbly, that these abrupt sec- tions are by no means confined to the coast, but are often formed on the ridges of the hills, at a distance from the sea. Ninthly, that in all such abrupt terminations of strata, whether on the coast or within land, the materials broken off are completely carried away, without a fragment being left behind.
The formation of these abrupt precipices has been, by some, as- cribed to the action of the sea : but it is only by careless observers, in Dr. Richardson’s estimation. that such an hypothesis can be ad- mitted; since even here the base of that part, which is perpendicular, is elevated 200 or 300 feet above the level of the sea; and the bases of others are no less than at 1400 feet elevation, and at the distance of four miles from the sea at Magilligan, of thirteen at Bienbraddock, and seventeen miles at Monyneeny.
The exact resemblance between the inland facades and those on the shore, proves them all to have been cut down perpendicularly by the same agent, which has not confined its operations to the coast, or to the periphery of the basaltic area. “We can trace it, says the author, over its whole surface.
Some persons have maintained that the inequalities are those of original conformation; as if the world had come from the hands of the Creator with all the varieties which now contribute so much to its beauty.
Others, admitting the original continuity of the strata, and their subsequent abruption, have differed concerning the direction in which the cause has acted; some preferring the milder and more gradual operation of waters from above the surface, which, according to Dr. Richardson, rather tend to level than to raise inequalities; while others conceive the highest mountains to have been blown up from the bottom of the sea by furious explosions, which, in the author’s
