202 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 7, 



of the surf on a level strand, or possibly the agitation of the water 

 by wind : both causes may have operated (figs. 6, 7)' I prefer 

 the first explanation, because there are so many instances in which 

 the direction of the lines of surf can be easily traced ; and the inter- 

 ference of one small current with another is often apparent in the 

 intersection of these sets of lines (fig. 8). They appear generally 

 to have been slight ridges, and the subsequent compression of the 

 rock has changed them into sharp-edged tabulae, and the furrows 

 into narrow depressed lines. It is to these wave-ripples, or surf- 

 lines, as they may be called, that I would now refer some of the 

 markings which before I thought were drainage-lines or runnels* 

 {loc. cit. pi. 4. f. 5). The specimens at command then were far less 

 perfect than those since obtained, and much more altered by pres- 

 sure. To any one familiar with the mode in which the tide creeps 

 in or out among the ripple-hollows on a very level strand, this expla- 

 nation will not be deemed unsatisfactory. Many specimens show the 

 direct action of the water producing straight, close, transverse ridges, 

 and fig. 8 shows the contending currents, caused probably by slight 

 obstructions, which were poured into the hollow in various directions 

 during the advance or retreat of the tide. 



In some cases the holes of the burrowing annelides have modified 

 the shape of the surf-ripples, in others they have been modified by 

 them. 



Sun-cracks, Pl.V. figs. 9 & 10. 



These were most unexpectedly found in great plenty on the west 

 side of Yearling Hill. The rock there is closely laminated, a hard 

 green flagstone of exceedingly fine grain (almost flinty), and the 

 rippled surfaces are covered with a filmy coating of dark-brown oxide 

 of iron. 



The sun-cracks do not differ to any great extent from those ordi- 

 narily met with in newer rocks (the Permian of Coventry, for instance). 

 They divide the surface into areolae of various sizes and shapes (fig. 9) ; 

 and when, as is most common, the superficial layer of mud is darker 

 than the stone, show themselves well in relief by exposing the lower 

 stratum. The edges of the areolae are most generally curved up- 

 wards, the heat of the sun having caused shrinkage. Sometimes this 

 is so much the case, that casts of them in relief, having a semi- 

 cylindrical form, and cut across by other smaller cracks, look very 

 like jointed portions of Crustacea ; and the resemblance is heightened 

 by frequent tubercles, which are the projecting casts of the annelide- 

 holes above noted. 



Rain-prints. PI. V. figs. 1 & 10. 



If the ripple-marks and the marks of shrinkage from sun-drying 

 be preserved upon these old surfaces, it is not unlikely that rain-prints 

 should be also present ; and accordingly numerous traces of the action 



* Not, however, those with branched or dichotomous furrows ; they must still 

 be considered as drainage-lines. 



