246 DR. C. T. TEECHMANN ON THE [vol. lxxix, 



12. The Jurassic Rocks of New Zealand. By Charles 

 Taylor Trechmann, D.Sc, F.CS. With an Appendix 

 on Ammonites from New Zealand, by Leonard Frank 

 Spath, D.Sc, F.G.S. (Read June 22nd, 1921.) 



[Plates XIL-XVIII.] 



Contents. 



Page 

 I. Introduction 246 



II. The Jurassic Plant-bearing Beds of New Zealand 250 



III. Description of Localities of Jurassic Rocks 251 



IV. Conclusions regarding the Age of the New Zealand Jurassic 



Deposits 256 



V. Relationship to the Jurassic Deposits of Adjacent Areas . 258 



VI. Palaeontology of the New Zealand Jurassic 258 



(«) Belemnitidae. 



(b) Gasteropoda. 



(c) Lamellibranchiata. 



(d) Brachiopoda. 



VII. Synopsis of the Fossil Moljusca and Brachiopoda hitherto 

 known or described from the Jurassic of New Zealand, 



facing 286 

 VIII. Appendix: On Ammonites from New Zealand 286 



I. Introduction. 



The Jurassic in New Zealand comprises a thick series of deposits, 

 important both stratigraphically and structurally. In every 

 locality where the. sequence is well seen they follow closely the 

 Triassic rocks with apparent perfect conformity. Compared with 

 the underlying Trias, however, they exhibit contrast in a number 

 of characters, among which are the following : — 



(«) They are, generally speaking, less steeply inclined and enter 

 less, so far as is at present known, into the structure of the Alpine 

 mountain-ranges. No instance is known to me where rocks with 

 recognizable Jurassic fossils occur in a slaty or semi-metamorphic 

 condition as do the Triassic rocks in some places on the eastern 

 fringes of the Southern Alps : for example, at Mount Potts and 

 Mount St. Mary. 



(5) The Jurassic, in contrast with the Trias, exhibits a much 

 greater vertical range of marine fossiliferous deposits throughout 

 its thickness, including horizons ranging from the lowest Lias to 

 the Kimmeridgian and Tithonian. The Trias, on the contrary, is 

 fossiliferous only in the higher beds, ranging from the Ladino- 

 Carnic to the Rhsetic. 



(c) Jurassic rocks apparently occur over a rather greater length 

 of the two islands than the Trias, although this is probably due 

 merely to accidents of outcrop and exposure, since Trias much 

 resembling that in New Zealand recurs in New Caledonia. The 



