42 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [-^W' ^"^f 



and, judging from the species contained within them, so far as I 

 have seen, they appear of modern origin, probably of the age of the 

 Older Crag. There is, however, no part of the Coralline Crag, now 

 existing, so thoroughly sihceous as is the matrix of these fossils ; it 

 more resembles, in lithological character, the sandstones at Lenham 

 in Kent, without the colouring matter of those masses. 



There are only two species of Mollusca from Lenham* that bear 

 any sort of similitude to, or could be compared with, those in the 

 sandstone-casts of the Red Crag ; the one a Pyrula and the other a 

 Pectunculus. Of the former, I have seen only a fragment, and it 

 could only be assigned generically ; and the latter belongs to a genus 

 in which there is great difficulty in determining a species, even 

 where numerous and perfect specimens can be obtained for that 

 purpose; this difficulty is, of course, much increased where casts 

 only, and those neither numerous nor perfect, are all we have to 

 depend on. 



In endeavouring to trace the sources whence these extraneous 

 materials have been respectively derived, there is not much difficulty 

 in indicating the greater part of the formations that have so contri- 

 buted. We find the London Clay in close proximity with deposits 

 of the Older Pliocene Period; the Chalk shows itself at no great 

 distance, both in Norfolk and Suffolk ; and the few Older Secondary 

 fossils may also have been brought from a not much greater distance 

 than the Western Coast of Norfolk. It is rather with respect to the 

 Middle Period of the Tertiaries that we are in some perplexity, if 

 the fossil Fish-teeth from Malta and Suffolk be truly identical. The 

 same may be said with regard to some of the Mammalian remains, 

 such as HijQjpotheriiim and Hycenodon ; presuming that they are 

 species of the Miocene Period. In this case we must have in the Red 

 Crag the contents of destroyed portions, not only of marine but also 

 of freshwater deposits of the Middle Tertiaries ; and, as the speci- 

 mens, of the marine animals at least, are by no means few in number, 

 the deposits that supplied them could not have been very remote. 

 The Limburg bedsf appear to make an approach to what we re- 

 quire for some of these fossils, and may perhaps have contributed a 

 portion. 



* See Quart. Journ. Greol. Soc. vol. xiv. p. 334. 

 t Quart. Journ. Greol. Soc. vol. viii. p. 298, &e. 



