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no less than 300 new species of ichthyolites, 50 of which have been 

 added since our last anniversary. He had previously pointed out 

 as a general law that particular generic types are strictly confined 

 to certain groups of strata, and it is remarkable that so vast an 

 accession of new species offers but few exceptions to the rule. 

 In the chalk two species have come to light belonging to genera 

 before observed in the oolitic series only, and a distinct species of 

 one of these genera extends even into the lower or Eocene tertiary 

 deposits. 



The labours of Mr. Charlesworth have thrown much light on the 

 structure of the crag of Suffolk and Essex, and on the fossils of 

 that deposit. He proposes to divide the crag into the upper or red 

 crag, and the lower or coralline crag, the last of which consists for 

 the most part of calcareous sand, derived chiefly from the decom- 

 position of zoophytes and shells, and in which many very perfect 

 corals and testacea are preserved. Among other places this coral- 

 line crag may be well examined at Tattingstone, Ramsholt, Orford, 

 and Aldborough. It is now many years since Mr, Wood, of Hes- 

 kerton in Suffolk, formed a large collection of crag fossils, amount- 

 ing in number to no less than 450 species of the classes Annulata, 

 Cirrhipeda, Conchifera, and Mollusca. Out of 370 species of shells 

 found in the lower crag, Mr. Wood identifies 150 with those found 

 in the red crag. Of these 150 species, common to the two deposits, 

 Mr. Charlesworth suggests that many may have belonged to the 

 lower bed and have been washed into the newer one, in the same 

 manner as some fossil shells of the chalk have been evidently im- 

 bedded in the crag. 



Such accidental mixtures have doubtless occurred, and they have 

 been occasionally remarked by geologists in other places under 

 analogous circumstances. But I continue to believe that these 

 upper and lower divisions of the crag should be referred to the 

 same geological period. The determination of that period or the 

 exact place which the crag should occupy in the chronological series 

 of European strata is a more difficult question. When I first sub- 

 mitted 111 species of crag shells to the examination of M. Deshayes, 

 he was of opinion that 66 of them were extinct, and that the others 

 belonged to recent species now inhabitants of the German ocean. 

 I lately laid before him 60 species from the coralline crag with which 

 Mr. Charlesworth had favoured me, and he was still of opinion that 

 the proportion of recent species was equally great. 



But I should add that the suites of individuals of each species 

 were not so full and complete as might have been desired, to enable 

 these identifications to be placed beyond all doubt. Dr. Beck 

 has lately seen 260 species of crag shells in Mr. Charlesworth's ca- 

 binet in London, and informs me, that although a large proportion of 

 the species approach very near to others which now live in our nor- 

 thern seas, he regards them as almost all of distinct species, and un- 

 known as living. Both he and M. Deshayes have declared the 

 shells to be those of a northern climate, and according to Dr. Beck 

 the climate may even have resembled that of our arctic regions. 



