Thomson. — Stage Nariies applicable to Divisions of Tertiary. 29 



Zealand place-names. The subdivisions of Hector and McKay's classifi- 

 cation followed the latter principle. 



The difficulties in the way of framing a classification that shall receive 

 general support are twofold. New Zealand geologists are not agreed as 

 to the presence or absence of unconformities between certain rocks, and 

 they are not agreed on the correlations that should be made between the 

 rocks of different localities. As a matter of fact, neither of these difficulties 

 need stand in the way of a classification by stages, provided that there is 

 agreement as to the order of superposition in the localities on which they 

 are based, and as to the order of preference of localities from which they 

 are named. 



It may be pointed out that the European time - scale (Cambrian, 

 Ordovican, &c.) is now entirely independent of unconformities, although 

 these were formerly used in drawing it up. There is no gap between 

 Jurassic and Cretaceous time, although in many parts of England there 

 are unconformities between Cretaceous and Jurassic, and again between 

 different divisions of the Jurassic. In other parts of England the missing 

 stages are represented. What we should aim at in New Zealand, then, is 

 a similar series of stage names corresponding to all the divisions of geo- 

 logical time represented in our rocks. If we can agree so far, a great 

 advance will be made in several directions. In the first place, although 

 the stages may be variously combined by different authors into geological 

 systems, the subdivisions of their systems wall remain the same, and the 

 points at issue will be easily grasped by those w^ho have not followed the 

 whole perplexing controversies in New Zealand literature. In the second 

 place, attention will be drawn to the lack of a satisfactory knowledge of 

 the fauna of many of the stages, a lack which largely explains the divergent 

 views hitherto held as to correlation. When this lack is supplied it will 

 be possible to compare the rocks of other localities with those chosen as 

 types for the various stages, and if important unconformities exist they 

 will either be detected by the absence of knowai stages in the new localities 

 or by the discovery of new stages unknown in the type localities. Such 

 a palaeontological solution, of course, cannot be expected in cases like the 

 Weka Pass, where one of the rocks — the Amuri limestone — is practically 

 without fossils, unless the microscopic fauna can be brought into use. The 

 subdivision of the Tertiary into stages, then, is not likely to advance greatly 

 the solution of the Cretaceo-tertiary problem in areas where the Amuri 

 limestone is developed, but should clear up our views on the stratigraphy 

 of the Tertiary rocks. 



In choosing localities and rocks to serve as types, and to give names 

 to the various stages to be recognized, it would be desirable to adopt the 

 principle of priority of mention in geological literature if this were prac- 

 ticable.* Names might thus be chosen from widely separated localities, 

 and the order of the stages then determined by a comparison of the faunas. 

 This method, adopted in Europe, South America, and Australia for the 

 stages of the Tertiary, has frequently created controversies as to the 

 equivalence or relative position of the various stages, and is undesirable 



* The following is the rule adopted by the United States Geological Survey on this 

 point (24th Ann. Rep., 1903, p. 24) : " In the application of names to members, forma- 

 tions, and larger aggregates of strata, the law of priority shall generally be observed, 

 but a name that has become well established in use shall not be displaced by a term 

 not well known merely on account of priority. In general, a newly defined formation 

 shall not receive a name that has been previously used in a different sense." 



