314 



RELATIVE AGES OF THE CRAG 



tion of the two deposits, which is sufficiently remarkable. — 

 The older or coralline mass is chiefly composed of commi- 

 nuted shells and zoophytes, the calcareous sand thus con- 

 stituted being divided by thin horizontal layers or flags of 

 impure limestone, which however are not continuous. It is 

 evident that the calcareous sand had acquired a certain de- 

 gree of consistency at the bottom of the sea, before the red 

 crag was thrown down, for it is seen to have been perforated 

 by numerous Pholades, the tortuous holes of which descend 

 six or eight feet below the top of the coralline crag, and still 

 contain the shells of the Pholas, while the remainder of the 

 cylindrical hollow has been filled with differently-coloured 

 sand derived from the superincumbent deposit. There is also 

 another proof of the inferior mass having obtained a certain 

 degree of consolidation before it was denuded. The loose 

 upper crag at Sutton does not rest everywhere on a level 

 foundation of subjacent coralline crag, but abuts abruptly 

 against a vertical wall or cliff of the older formation, as shown 

 in the annexed diagram (fig. 39). This buried cliff, eight or 



Eed Crag. 



Coralline Crag. 



ten feet high, may be traced at Sutton, running in a direction 

 N.E. and S.W., and in some spots may be seen slightly over- 

 hanging. In consequence of this circumstance, a deceptive 

 appearance of distinct alternations of red and coralline 

 crag is often produced, when a vertical section, parallel to 

 the line of junction, is laid open. Even where the buried 

 precipice of coralline crag has not been perpendicular, but 

 merely having a very steep slope, an artificial cut at a high 

 inclination may so intersect alternately the red and coralline 

 crag, as to lead to the conclusion which I first entertained at 

 Sutton, of a real intercalation of the two formations. Some 

 of the apparent anomalies seen in like manner in the stratifi- 

 cation of the red crag, may sometimes be ascribed to the de- 

 position, on the steep sloping sides of submarine sand-banks, 

 of new matter of a different colour and composition. When 

 these are afterwards cut through in the steep slope of a sea- 

 cliff, we occasionally see patches of the more modern bed 

 adhering like plaster to the face of the older one. 

 At Tattingstone, in Suffolk, the inferior or coralline crag 



