Park. — The Lower Mesozoic Rocks of Neio Zealand. 391 



shall end and the Jurassic begin. And, after all, it is not 

 a matter of very great importance whether we classify this 

 great pile of strata as wholly Triassic or partly Triassic and 

 partly Jurassic. The stratigraphical relations of the different 

 beds must always remain the same wherever they are placed 

 in the geological scale. On the other hand, the well-defined 

 limitations of the Trias in Otago and Nelson leave little doubt 

 that the Clyde River beds should be correlated v^^ith the 

 Mataura and Maitai formations of Jurassic age. 



Triassic Marine Rocks. 



The position of the marine zones associated with the 

 Triassic beds at Nelson, Hokonui Hills, and Nugget Point 

 have now been accurately determined. The character and 

 thickness of the sediments separating the zones were neces- 

 sarily governed by the local conditions prevailing at the time 

 of deposition, and therefore are found to vary greatly in the 

 different basins; but the succession and relative position of 

 tiie zones are always the same, clearly indicating that the 

 different basins were connected by a continuous sea. 



The zones contain a number of characteristic forms of 

 fossils, and many of the species have been determined. Where 

 the species have not been determined the genera of the 

 Brachiopoda are often sufficiently distinctive for correlative 

 purposes. 



The prevalence of Brachiopoda in the lower and higher 

 marine zones is conspicuous in all the Triassic basins through- 

 out New Zealand. 



Jurassic Marine Rocks. 



The marine zones associated with the Jurassic beds of 

 New Zealand are few in number and seldom rich in fossil 

 forms. Characteristic fossils are rare, and the majority of 

 the species have not yet been determined. 



In his survey of the Hokonui Hills, in 1878, Mr. Cox sub- 

 divided the Jurassic rocks into four different groups or series 

 of beds, but a subsequent examination which I made of his 

 sections showed that his groups contained no characteristic 

 marine zones, while in some cases they were found to overlap 

 each other. Groups that cannot be identified in their typical 

 localities are necessarily valueless for purposes of correla- 

 tion. 



The brachiopods which are so abundant in the Upper 

 Trias in Nelson and Nugget Point basins are sparingly repre- 

 sented in the overlying marine zones of the Jurassic ; and 

 gasteropods are equally rare. 



As late as 1899, Captain Hutton attempted no subdivision 

 of the Jurassic rocks, and in the absence of sufficient data I 



