60' UNCONFORMABLE STRATIFICATION. [Ch. V 



and disturbed. Afterwards the upper series was thrown down in hori- 

 zontal strata upon it. If these superior beds, as d, d, fig. 83, are also 

 inclined, it is plain that the lower strata, a, a, have been twice displaced ; 

 first, before the deposition of the newer beds, d, d, and a second time 

 when these same strata were thrown out of the horizontal position. 



Playfair has remarked* that this kind of junction, which we now call 

 unconformable, had been described before the time of Hutton, but that 

 he was the first geologist who appreciated its importance, as illustrating 

 the high antiquity and great revolutions of the globe. He had observed 

 that where such contacts occur, the lowest beds of the newer series very 

 generally consist of a breccia or conglomerate consisting of angular and 

 rounded fragments, derived from the breaking up of the more ancient 

 rocks. On one occasion the Scotch geologist took his two distinguished 

 pupils, Playfair and Sir James Hall, to the cliffs on the east coast of 

 Scotland, near the village of Eyemouth, not far from St. Abb's Head, 

 where the schists of the Lammermuir range are undermined and dis- 

 sected by the sea. Here the curved and vertical strata, now known to 

 be of Silurian age, and which often exhibit a ripple-marked surface, are 

 well exposed at the headland called the Siccar Point, penetrating with 

 their edges into the incumbent beds of slightly inclined sandstone, in 

 which large pieces of the schist, some round and others angular, are 

 united by an arenaceous cement. " What clearer evidence," exclaims 

 Playfair, " 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 of 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 epoch still more remote pre- 

 sented 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."f 



In the frontispiece of this volume the reader will see a view of this 

 classical spot, reduced from a large picture, faithfully drawn and colored 

 from nature by the youngest son of the late Sir James Hall. It was im- 

 possible, however, to do justice to the original sketch, in an engraving, as 

 the contrast of the red sandstone and the light fawn-colored vertical schists 



* Biographical account of Dr. Hutton. 



f Playfair, ibid. ; see his Works, Edin. 1S22, voL iv. p. 81. 



