2\S Mr. Hunton's Remarks on a Section of 



not only the species and genera, but the order of Testacea have undergone a 

 total revolution. Instead of a preponderance of Cephalopods and a scarcity 

 of bivalves, we now have an overwhelming majority of the latter, some of the 

 beds being almost constituted of Cardia and Gryphytes, which have also an 

 extensive vertical distribution. Avicula Cygnipes, A. inaquivalvis and Pul- 

 lastra antiqua are equally abundant in the whole series ; but other shells, 

 as Cardium truncatum, occur more plentifully in the inferior strata, whilst 

 Terehratula tripticata and T. trilineata crowd the superior. 



The species of Ammonites, though few in number, are, however, highly 

 characteristic ; thus we find A. vittatus about the centre of the series, con- 

 fined to a very small range, associated in nodules with the Cardium multicos- 

 tatum. Turbo undulatus, and Pecten planus ; but the two latter occur in other 

 parts of the formation. The A. maculatus, is constantly found at the junction 

 of the marlstoue with the lower lias, which here pass so gradually into each 

 other, that it is impossible to determine where the sandstones end and the 

 blue shale begins. I have long sought for A. maculatus in the upper and 

 central portions of the TwoWsfone, but have never found it many feet above 

 the junction beds ; and though this and other Ammonites from unequal geo- 

 graphical distribution, may be more abundant in one place than in another 

 (A. maculatus is in greatest number at Staithes, A. Hawskerensis at Haws- 

 kerbottoms), yet they constantly maintain an invariable relative position. A. 

 Hawskerensis I believe to be also a junction Ammonite, but from its rarity in 

 other situations, than that mentioned, it is not entered in the table. 



The above description may not, in some instances, exactly accord with pre- 

 vious statements, but one great source of error has hitherto been, the collect- 

 ing of specimens from the debris of the whole formation, accumulated at the 

 foot of cliff's or other similar situations, where they have long laid, and the 

 inferring of their position from the nature of the matrix. A strong tempta- 

 tion to this method arises from the facility it affords of obtaining finer fossils 

 than can possibly be procured from newly quarried nodules, the hard nature 

 of which renders it very difficult to extract the fossil entire, without long 

 exposure to air and moisture. 



Annexed is a systematic list of the fossils found in the upper lias and marl- 

 stone, and noticed in the section. 



