INTRODUCTION. 



The Red Crag. 



1. Its structure. — The physical structure of the Red Crag is unlike that of any other 

 formation known to us, ancient or modern. The more considerable portion of it is 

 formed of a succession of beds, varying from two or three, to nearly twenty feet in 

 thickness, each of which consists of laminae of sand and shells, inclined at a high degree 

 to the horizon. The laminse planes of each bed form an angle with those of the other beds 

 above and beneath them ; and at the base of each bed they change into a slight curl. 1 

 This structure is altogether different from the well known one of false bedding, which 

 also exists in some parts of the Red Crag, especially in that under which the phosphatic 

 nodules are worked, and the two forms of bedding pass more or less into each other. 

 This oblique lamination may be traced (as, for instance, in BaAvdsey Cliff) for a consicler- 



OBLIQTJE RED CRAG IN BAWDSEY CLIFF. 



The oblique bedded crag appearing above the Talus is nearly twenty 

 feet in thickness. 



able distance in a constant manner, without shading off into horizontal stratification 

 or passing into false bedding. If we examine a section of any beach or foreshore 

 (at right angles to the line of the shore) we shall find it presents exactly this 



describes eighteen species, of which only five are recognised as living, viz. Cythere punctata, C. sublacunosu, 

 C. trachypora, Cythereis ceralopfera, and C. tamarindus ; the first and fourth of which are species of the 

 British coasts, the third and fourth of the Norwegian coast, and the fifth an Atlantic form. Of the Poly2oa 

 their describer Mr. Busk says, in a letter to the author of the 'Crag Mollusca,' "Judging from the habits of 

 existing forms, those of the Crag may have lived at any depth from the surface downwards," to which we 

 may add that the rock bed made up of the remains of Polyzoa is very false-bedded, which is indicative of 

 the reverse of deep water. 



1 Something approaching this oblique lamination may be seen in the Great Oolite of the Great Northern 

 Railway cuttings near Grantham, and on the Yorkshire coast south of Scarborough. 



