73 



sections, &c. The boundary between tbis and tbe preceding 

 stratum is not very distinct, when viewed closely ; but is quite 

 conspicuous when seen from a short distance. Throughout 

 their whole vertical extent the part of the cliff, formed by 

 these clays, exhibits when dry a vertical cleavage like starch. 

 The .enclosed fragments in the bands of sand and gravel are of 

 all sizes and degrees of wear, notwithstanding the difference of 

 hardness of such rocks as granite, mica slate, &c, and suggest 

 the idea that the whole has not been transported hither from 

 distant localities, but produced by the chemical disintegration 

 of a previous rock of lower Micene or upper Eocene age, as 

 testified by the fact that the largest fragments occur at almost 

 regular levels, containing numerous* fossils and casts, princip- 

 ally of Turritella Aiding ce (Tate), characteristic of the succeeding 

 layer, to be described hereafter. The whole being strongly 

 impregnated with saline ingredients, everywhere perceptible to 

 the taste, and frequently forming a glassy crust upon the face 

 in protected localities, appears to strengthen materially this 

 assumption. "What these saline substances are, has not been 

 ascertained, but they do not appear to consist of pure chloride 

 of sodium ; efflorescences of these have been observed forming 

 stars of needle-like crystals, colourless, transparent, and 

 diverging under a low angle. Some Turritellce^ &c, and an 

 Echinus have been.found at various levels, and not damaged by 

 rolling or grating, which would have been the case had. they 

 been carried hither by currents of water. Having observed 

 these clays in one locality overlying the succeeding bed conform- 

 ably, at another abruptly taking the place of the upper portion 

 (figs. 4 and 5) thereof, has induced me, together with the other 

 observed facts mentioned above, to consider them as the upper- 

 most member of the Older Tertiary strata. Their maximum 

 thickness does not exceed, where observed, fifty feet, while the 

 parallel average may be about twenty-five to thirty -five feet. 



Turritella Grits. — Ascending from Ardrossan any of the 

 neighbouring low hills we meet near their summit with frag- 

 ments of a peculiar fossiliferous rock, the " Turritella grits," 

 as I propose to name it. It is a silicious rock of very variable 

 aspect, passing in density through all stages between opaline or 

 chalcedonic grit to soft, friable sand-rock, most frequently 

 having an intermediate character, very hard and very brittle. 

 Near Ardrossan and northward to Clinton (15 miles), it occurs 

 near the summit of the hills, occasionally capped by the 

 travertine limestone, seemingly in no relation to the clays, as 

 no section is available in loco. But southward between Rogue's 

 and Muloowurtie Points (fig. 4) the same rock appears (in the 

 beautiful section represented by fig. 5, and forming miles of 

 romantic cliffs) under the foregoing strata in its own true 



