308 PEOCEEJJINGS OF THE GEOLOGICAL SOCIETY. [May 22, 



undertook a critical examination of the species, which I think have 

 been too hastily regarded as differing from known forms. 



Mr. Tawney claims the Sutton Stone as lihsetic*, and believes it 

 probable that the Sutton series was slightly anterior in time to the 

 Avicula-contorta series. These inferences as to its age are based 

 solely on the following palaeontological premisses : — 



(1.) That Plicatula intusstriata is exclusively a Rhgetic fossil. 



(2.) That the absence of the usual Liassic species of Ammonites is 

 confirmatory of the Pre-liassic age of the beds. 



(3.) That many of the species have been noticed in the Rhsetic beds 

 on the Continent, or show strong affinities to the Upper Triassic fauna. 



That these premisses are faulty I will endeavour to prove. And, 

 first, as to the statement that Plicatula intusstriata is "a shell 

 acknowledged to be characteristic of the Hhaetic series, and never, I 

 believe, really found out of it " f. This shell is, in fact, quite as cha- 

 racteristic of the lower part of the Lower Lias as it is of the Avicula- 

 contorta series. In the east of France it occurs in the zones of 

 Belemnites aeutiis, Ammonites bisulcatus, and A. angulatus, in the 

 last of which it is common at Charleville, Moselle. Dumortier 

 states that it is one of the most characteristic fossils of the Ammo- 

 nites-jolanorhis zone of the Bassin du Ehone. It occurs in Great 

 Britain in other than the Avicula-contorta series, and in the Sutton 

 Stone at Island Magee, co. Antrim, whence I have obtained it in 

 the zone of Ammonites angulatus, — at High Lyme, Dorset, whence I 

 have seen specimens in the collection of Mr. Bott, attached to 

 Gryplicea incurva, — at Bridgend, specimens from which locality, ob- 

 tained from the interpolated shales in the Bucklandi-series, I have 

 examined in the collection of Dr. Miliigan. 



Secondly, as to the absence of the usual Liassic Ammonites. This 

 negative evidence is of no moment, inasmuch as Ammonites are few 

 in number as regards species in the Hettangian series of beds. It is 

 rare to find more than two or three species in one locality, though 

 these are sometimes represented by numerous individuals ; but two 

 species of Ammonites are recorded from the Sutton Stone which are 

 allied to the " Planorbes." Thus this positive evidence, slight as it 

 is, points rather to the probably Liassic age of the deposit. 



Thirdly, as to the Ehsetic and Triassic affinities of the species. 

 That the position assigned to the Sutton Stone is at variance with Mr. 

 Tawney's own palaeontological determinations is patent to all, when 

 the list of species from the Sutton Stone is compared with that of the 

 species from undoubted Avicula-contorta beds as given by that 

 author. The only species common to the beds in question are 

 Myophoria postera, Monotis decussata, and Plicatula intusstriata, 

 which last I have stated to pass uj) high in the Lower Lias. May 

 there not be some mistake with the others, perhaps inadvertently 

 ranked among the Sutton-stone fossils J ? Thus, on the author's own 

 showing, the fauna of the Sutton Stone is not Rh£etic ; but a careful 

 study of the fossils has led me to regard it as Liassic, and I ofi'er the 



* Loc. cit. p. 72. t lb. p. 78. 



I The ^ opposite Gyrolej^is Alberti, in the column headed Laleston, refers to 

 Micaittla intusstriata. 



