170 L. F. Spath — Notes on Ammonites. 



by this boring that there are over 300 feet of Coal-measure strata 

 beneath the Brockwell in South Durham which do not contain any 

 Ganister. This rock only occurs in the lower part of the series. 1 



Samples of the most interesting rocks brought up in the Cotefleld 

 Close boring are deposited in the geological laboratory of the 

 Armstrong College. 



I should like here to lay stress upon the necessity for the exami- 

 nation of all cores of borings by geologists. The record given by the 

 borers, especially in .such rocks as the Magnesian Limestone, is often 

 of little value for exact scientific work, and valuable information is 

 thus lost. 



IV. — Notes on Ammonites. 



By L. F. Spath, B.Sc, F.G.S. 



IV. 



fllHE variability and occasional instability of the Ammonoid 

 1 suture-line, to which attention has been drawn, the recurrence 

 of similar types, and the frequent asymmetry of the opposing halves 

 of a given suture-line, which is apparent not only in the Bactylioceras 

 commune, figured by Swinnerton & Trueman (fig. 9 on p. 42), but 

 also in the development of the suture-line in e.g. Psendosageceras 

 multilohatum, Noetling, 2 in Indoceras balnchistanense, Noetling, 3 or in 

 Oxynoticeras oxynotum, Qnenstedt, sp., 4 to mention only a few well- 

 illustrated examples, might be thought to impair the usefulness of 

 the suture-line for the classification of Ammonoids. Yet, long 

 before there was any subdivision of "Ammonites" at all, the greatest 

 importance had been attached to the foldings of the suture-line, and 

 Pictet stated in 1854 that "the lobes in their essential traits 

 furnished very constant and very valuable characters ". 5 Von 

 Buch's group of li Arietes' n Avas well characterized by the general 

 plan of the suture-line, namely, the deep siphonal lobe and the short 

 external saddle, only most authors would put more reliance on the 

 ornamentation of the shell and put such a form as Asteroceras 

 sagittarium, Blake, sp., into the genus "Aegoceras ". The writer would 

 even go so far as to say that the type of suture-line given by 

 Mr. Buckman 6 for "Defossiceras' n defossum, Simpson, sp., shouldnotbe 

 found at the horizon stated, 7 and that the form probably will turn 

 out to be an Arietid (Agassiceras) of semicostatum age. 



1 The borehole at Sheraton appears also to have entered theGaftister Series. 

 Thick beds of sandstone have been penetrated dipping at an angle of 45°, 

 probably northwards, as shown in section. 



2 " TJntersuchungen ii. d. Bau d. Lobenlinie v. Pseudosageceras multi- 

 lobatum, Noetling " : Pakeontographica, vol. li, pts. v, vi, 1905. 



3 "Die Entwicklung v. Indoceras buluchistanense, Noetling": Geol. u. 

 Pal. Abh. v. Koken, N.F., vol. viii, pt. i, 1906. 



4 "Die Entwicklung v. Oxynoticeras oxynotum, Que.": Geol. u. Pal. 

 Abh. v. Koken, N.F., vol. viii, pt. iv, 1908. 



5 Op. cit., vol. ii, p. 669. 



6 Yorkshire Type Ammonites, vol. ii, pt. x, p. 76, pi. lxxvi, 1913. 



7 Definitely given as ' ' capricomum zone " in Mr. Buckman's " Palseonto- 

 logical Classification, etc.", in The Geology of the Country between Whitby and 

 Scarborough (Mem. Geol. Surv.), 2nd ed., 1915. 



