88 Mr. Charlesworth on the Crag-formation 



An interesting circumstance connected with the organic 

 productions of the coralline crag, is the presence of a larger 

 number of the Echinidce than generally appear to have existed 

 during the formation of tertiary strata. I have not yet ascer- 

 tained the precise amount of species, but they include the fol- 

 lowing genera, Echinus, Cidaris*, Scutella, and Fibularia; the 

 last also occurs in the upper strata. 



The teeth of fish are distributed in considerable abund- 

 ance throughout the greater part of the red crag in Suffolk : 

 most of them exactly resemble the teeth so frequently met 

 with in the London clay of the Isle of Sheppey and other 

 places, and which probably belong to fish allied to the genus 

 Squalus. 



In the crag these teeth have undergone some peculiar che- 

 mical change, which has given them a dark colour, and ren- 

 dered them extremely hard ; they are generally much worn, 

 and exhibit a brilliant polish, which sometimes extends over 

 that portion formerly surrounded by the alveolar cavity. 

 Mr. Wood remarks, that he has found a few teeth of cartila- 

 ginous fish in the coralline crag : I have only seen two speci- 

 mens from it, but they had the enamel perfect, and presented 

 that delicate pearly lustre, shown by the teeth which occur in 

 the tertiary beds of Malta, and from which locality I should 

 certainly have supposed them to have been obtained, if I had 

 not been previously acquainted with their history. 



It is usually considered that the remains of land animals 

 are more or less blended with the marine productions of the 

 crag. Flattened portions of bone of a very compact struc- 

 ture, highly polished by attrition, and having their specific 

 gravity much increased, are often picked up on those parts of 

 the coast where the crag has been exposedf: with this ex- 

 ception, the instances of Mammalian remains occurring in the 

 Suffolk beds are extremely rare. 



ance described by Professor Phillips, while the deviations in the lower de- 

 pend upon the unequal distribution of shells and corals, either of which 

 predominating, occasions an alteration in the nature of the deposit. 



Mr. Taylor says that in Essex the crag shells sometimes occur in " strong 

 blue clay." I think that he must have derived this idea from Smith, who 

 in his * Strata Identified', uses precisely the same expression, probably con- 

 founding the crag with another formation. 



• The occurrence of this genus is stated on the authority of Mr. Taylor, 

 who in describing some of the corals from the crag, mentions a Cidaris as 

 being attached to one of them. See Loudon's Magazine of Natural History 

 for 1830, page 274. 



t These fragments have lost all character of the animal, or even parti- 

 cular bone, to which they belong. They may possibly be exterior portion* 

 of the femur of the elephant. 



