92 Mr. Charlesworth on the Crag-formation 



to inquire what was the probable extent of the period which 

 intervened between the formation of the coralline and the de- 

 position of the red crag. 



In the divisions now so generally adopted of the tertiary 

 formations, the crag has been placed among the older Plio- 

 cene ; I need hardly remark, that these divisions are founded 

 upon the relative proportion of fossil shells which agree with 

 existing species. The series of fossils from the crag examined 

 by M. Deshayes amounted to only 111, and of these 66 were 

 pronounced by him to be extinct. I much regret that at pre- 

 sent no examination of this kind has been made of the newly 

 discovered shells; they will probably by found to include a 

 larger proportion of extinct species, and perhaps to an 

 amount that would indicate their belonging to a period of 

 higher antiquity than the Pliocene*. 



In some parts of Suffolk, shells are found in the alluvial 

 soil identical with those now inhabiting the German Ocean, 

 and which have no connexion with the crag; these are pro- 

 bably contemporaneous with the brick earth of the Nar, a de- 

 posit in Norfolk evidently of recent origin. It is therefore 

 of the utmost importance, in the examination of tertiary shells 

 from these districts, to obtain accurate information of the 

 precise localities in which they were procured. 



Mr. Woodward describes the Norfolk crag commencing 

 at Weybourne and Cromer, and running in a narrow band 

 across the eastern part of the county. There is one circum- 

 stance that appears to me particularly worthy of attention 

 connected with the amount of species obtained from this part 

 of the formation : 



As nothing analogous to the coralline crag has been ob- 

 served in Norfolk, the deposit may there be looked upon as 

 agreeing with the red crag of the adjoining county. On 

 looking over the list of shells obtained by Mr. Woodward 

 from the neighbourhood of Norwich, I find it contains only 

 80 species, while the upper or corresponding beds in Suffolk 

 have furnished 235 : this difference we should not have anti- 

 cipated. If, however, the sandy strata of the coralline crag 

 formed in Suffolk a bed for that ocean which in Norfolk 

 rested on the chalk, the apparent inconsistency may be easily 



* A comparison of Mr. Wood's collection with a recent series of British 

 shells must be looked forward to with the greatest interest. With regard 

 to the age of the crag, the question should first be settled, whether or not the 

 two deposits indicate different periods. If the organic remains of each are 

 considered separately, theie will be some difficulty in determining the age 

 of the upper one, unless the suggestions I have thrown out respecting 

 some of its shells be overruled. 



