174 ME. C. THOMPSON ON THE [Julie I913V 



Oxynotus Beds. 



The derived fossils torn from the Oxynotus Zone — applying the 

 term in the inclusive sense, as used by Tate & Blake 1 — represent 

 well all three divisions. 



Most of the characteristic forms are found. Xipluroceras plani- 

 costa occurs in very hard stones, which may only be the ground- 

 down remains of nodules. Asteroceras obtusum is generally found 

 in fragments free from matrix, as if from shales similar to those 

 of its bed in Robin Hood's Bay. The same remark applies also 

 to A. sagittarium. The spinate examples of Wright's Xiphero- 

 ceras planicosta are also present, but appear to be rare. Oxy- 

 noticeras is fairly well represented. 



On coming, however, to the raricostatum division, many hard 

 blackish blocks are found, full of specimens of Ecliioceras. These 

 blocks remind one of the semicostatum limestones, and, in conse- 

 quence of the abundance of examples obtained, the appended list 

 (p. 180) shows comparatively many new forms for Yorkshire. No 

 such limestone is mentioned by Tate & Blake. Simpson's E~ 

 exortum is merely cited as found in Robin Hood's Bay. 



In regard to Asteroceras accderatum Hyatt, a short paper by the 

 present writer appeared in the ' Naturalist ' for June 1910. 



One most interesting find, early in this search, was a block of 

 tough limestone containing numerous specimens of the young of 

 Blake's Asteroceras sagittarium most beautifully preserved. Anyone 

 who has found that ammonite in place at the above celebrated bay 

 knows to his sorrow that such is not the case there. When these 

 small specimens and their matrix were submitted to Mr. Buckman 

 some years ago, he at once suggested the probability of the block 

 having come from the east, and not from the well-known exposure 

 of shales at Robin Hood's Bay. 



Altogether, the list shows, for these lowest zones, 

 a much closer resemblance to the ammonite fauna of 

 the South German Lower Lias than any previous one 

 published for Britain. 



Seeing that the zones so far enumerated present so many new 

 forms; that the limestones cannot be matched now in Yorkshire ; 

 also that they have never been definitely recognized by collectors in 

 that area, although their presence has been assumed, I am forced 

 to the conclusion that, either the sea has destroyed outcrops once 

 exposed of these hard limestones, or the ice plucked them from 

 outcrops in the bed of a former North Sea. 



I would urge the latter conclusion. 



Armatus-jamesoni Beds. 



For some years my colleague and I could not find a single 

 representative ammonite from the Armatus-jamesoni Zone, although 

 fragments of the characteristic small belemnites had been found 



1 ' The Yorkshire Lias ' 1S76, p. 72. 



