IV. — GEOLOGY. 



Art. XXX. — On the Subdivision of the Loiver Mesozoic 



Jrlocks of Nero Zealand. 



By Professor James Park, F.G.S., Director Otago Univer- 

 sity School of Mines. 



\^Read before the Otago Institute, 11th August, 1903.] 



Plates XXVIII. to XXXI. 



Introduction. 



An examination of the Trias in Nelson, Southland, and 

 alpine Canterbury has led me to the conclusion that the 

 subdivision and correlation of the horizons of this formation 

 present a much more difficult problem than hitherto supposed. 

 Not only do the rocks occur in many disconnected basins, but 

 even in what appears to have been a continuous basin the 

 strata have been so wasted by denudation or disturbed that 

 it is often impossible upon stratigraphical grounds to corre- 

 late group with group except within a very limited area. To 

 these difficulties there is added a wonderful uniformity of life 

 throughout the system ; and, although the assemblages of life 

 in claystone and sandstone often possess distinctive forms, 

 there is evidence in some places that repetitions of similar 

 conditions of deposition had been attended with a reappear- 

 ance of the life characteristic of those conditions. 



The minor subdivisions of a formation are only of local 

 value when the limits of characteristic life and stratigraphical 

 connection can be seen to coincide. It is evident that a classi- 

 fication is of little value that follows too closely the great sub- 

 divisions as they occur in Europe, subdivisions, perchance, 

 grouped on the mere presence of a few genera whose asso- 

 ciation in a particular horizon may have been the result of 

 peculiar local conditions prevailing at the time of deposition. 



It has been shown, both by geologists and palaeontologists 

 alike, that there is a singular lack of homotaxial parallelism 

 between the marine and terrestrial organisms of Australasia 

 and Europe, which, moreover, seems to become more marked 

 and significant as we advance through the Mesozoic and Ter- 

 tiary periods up to the present time. For example, there is a 

 greater characteristic relationship between the Secondary flora 

 •of Australia and the Carboniferous of Europe than there is 



