1849.] PRESTWICH ON THE CRAG AT CHILLESFORD. 351 



Should the identity of these beds with the mammaliferous crag of 

 Norfolk be proved, then the evidence as given in this one locality by 

 superposition will be in perfect accordance with the triple division 

 of the crag established by Mr. Charlesworth. Still 1 would direct 

 more particular attention to the precise relation which the red crag 

 may bear to this deposit, and to the exact determination of the phse- 

 nomena at their junction, of which we did not meet with a satisfactory 

 exhibition. 



Of the 23 species enumerated by j\Ir. Wood, I find according to 

 Prof. Forbes's catalogue*, in his 'Report on the geological relations of 

 the existing fauna and flora of the British Isles, that 10 occur in the 

 coralline cragf, 21 or 22 m the red crag, 22 or 23 in beds of the age 

 of the Clyde pleistocenes, and 22 exist in the present seas of Green- 

 land or on our own coasts. Only 1 or possibly 2 species out of the 

 23, viz. the Nucula CobboldicB and one of the Tellines probably, do 

 not occur recent. 



With the Bridlington beds this group shows but few species in 

 common, probably not more than 6 or 7. It thus appears that, 

 with the exception of one or two, the whole of the species associated 

 together in this bed, range from the period of the red crag to that 

 of the present day ; 8 or 9 were congeners at the period of the coral- 

 line crag with forms of a more southern character ; but now the far 

 larger proportion of the entire group are inhabitants of the northern 

 seas, and a small portion of them only range to the Celtic, and still 

 fewer to the Lusitanian regions. Altogether, the aspect of the fauna 

 may be certainly considered as northern. This fact, however, as the 

 period is probably the one immediately preceding the great northern 

 drift, when there may have been open seas to the north, I should 

 rather be inclined to ascribe to the lower temperature of the waters, 

 arising from the existence of currents from the northern seas, than to 

 consider it as evidence of a land temperature much different from 

 that of the present day. 



Further, although many of the species are very typical, the number 

 common to several periods forms too large a proportion of the total 

 for us to arrive at present at a very accurate estimate of the exact age 

 of these beds. That they are comparatively of recent date, is indicated 

 both by organic remains and by superposition, but our knowledge of 

 their fauna ought to be considerably extended, and I believe that the 

 means of doing so exists, before the exact position of these beds can 

 be determhied. It is, however, evident that they are more recent 

 than the red crag, and older than the great northern clay-drift, which 

 thus reduces the question to within comparatively narrow limits. 



Since writing the above, I have been led to consider, from the want 

 of a more general agreement between the fauna of this deposit and 



* Memoirs of the Geological Survey of Great Britain, vol. i. p. 406. 

 + This includes the Turritella terebra, which Mr. S. AA'ood gives only from the 

 red crag. 



