300 PROCEEDII^GS OF THE GEOLOGICAL SOCIETY. [May 22 



(3.) Glenarm. — Beds of the horizon of the Ammonites -jplanorhis 

 zone are seen in the Little Deer Park, one mile south of Glenarm, 

 where the following succession can be made out : — 



a. Black shales with a few bands of grey argillaceous sandstones, 



with Sehizodus cloacinus, Avicula contorta, &c. 

 h. Grey and yellow marly sandstones. 



c. Black, shelly, laminated sandstones, with Osirea iry^egularis. 



d. Blue clay, with nodular and bedded shelly limestones containing 



Ammonites Jolmstoni. 



Beds h and c represent the zone of Ammonites planorhis ; whilst 

 the shales of series a are referable to the Avicula- contorta beds, 

 which comprise a large moiety of the whole section, having a 

 thickness of about 40 feet*. 



(4.) Oarr on Point. — Here the " Planorbis-series " is represented 

 by stiff shales, with the characteristic Ammouite, interposed between 

 the Avicida- contorta shales and the limestone and arenaceous beds 

 of the zone of Ammonites angulatus with Cardinia ovalis. The Lias 

 is very much reduced in thickness, and entirely disappears on ap- 

 proaching the entrance to Glenariff Glen, to the west of this locality. 



(5.) Portrush. — The remarkable and isolated mass of Lias at this 

 place, which has been the subject of much discussion, consists of 

 porcellanous shales, being the extreme of alteration f of the soft 

 shales of the " Planorbis-zone " at Colin Glen and elsewhere, of 

 which metamorphoses indurated shales of the same horizon at 

 "Waterloo are the first result. 



Oppel J, writing of the " Schichten des Ammonites angidatus/' 

 states that " these beds appear to exist in the north of Ireland, and 

 certainly on the coast at Portrush, from which locality I have seen 

 in the collection of Professor John Morris an example of an 

 undoubted Ammonites angulatus ^ IS'ow the presence of a single 

 specimen of this Ammonite is no evidence that the bed from which it 

 was obtained belongs to the zone of Ammonites angidatus, as this 

 species ranges up into the zone of Ammonites Turneri, whence I 

 have obtained it, at Ashley, near Bristol. 



I take this opportunity to explain the meaning I attach to the 

 term zone. The Lias can conveniently be subdivided into zones or 

 stages, characterized by organic remains, and generally by hthologieal 

 features, the former being more or less a consequence of the condi- 

 tions which produced the latter ; and thus the zones mark different 

 conditions of sea-bottom and of life. Species of Ammonites being 

 the most restricted in range of the common fossils of the Lias, and, 

 moreover, easily identified, have been selected as indices to tlie zones ; 

 but their presence alone does not warrant us in assigning this lime- 

 stone to the zone of Ammonites angidatus, or that clay to that of 



* North of Glenarm, as at the Deer Park, the Avicula-contorta zone contains 

 a limestone band with Cardium Bhcsticum, and a meagre representative of the 

 bone-bed in the neighbourliood of Belfast. 



f "The true Position of the Metamorphosed Lias was established by Bryce," 

 Portlock, Eep. on Geol. of Derry, p. 97 (1843). Vide Dr. Bryce's paper. 



\ Juraformation, p. 34. 



