442 Transactions. — Geology. 



confusion it would, I think, be preferable to drop the term 

 "Maitai" and adopt the name " Mataura " for all rocks of 

 Jurassic age throughout the colony. 



Captain Hutton, in his report of 1873, referred the Maitai 

 formation to the Jurassic system ; and now, after a lapse of 

 thirty years, it is necessary for me to bring it back to the 

 position then assigned to it. The Carboniferous age of the 

 Maitai rocks imposed many insoluble problems on the geology 

 of New Zealand. The removal of the Maitai formation to 

 its natural position in the Jurassic now paves the way for a 

 systematic subdivision of the Lower Mesozoic rocks of New 

 Zealand. 



Conditions of Deposition of the Nelson Trias. 



The presence of plant-remains and of Mytilns in the finer 

 sediments, and of Patella and saurian bones in the coarser 

 sandstones and conglomerates, points to a prevalence of 

 shallow-water conditions of deposition from the beginning to 

 the end of the Trias period in the Nelson basin.* 



Myukcs is essentially a littoral shell. In some horizons it 

 occurs in millions, and in a condition of preservation that 

 clearly shows that the shells were buried in the sediments 

 accumulating around the places where ttieir owners had lived. 

 It is therefore certain that the old marine littoral of the 

 Palseozoic land-surface on the shores of which these Mytilus 

 deposits formed was where these fossils now abound — that is, 

 along the southern boundary of the Waimea Plain. 



The shallow-water character of the fossil shells and the 

 alternating marine muds and river-detritus indicate that the 

 local conditions of deposition were fluvio-marine, or, at any 

 rate, of such a nature that during abnormal floods , or through 

 the formation of shoals causing a diversion of the ordinary 

 currents, river-detritus became mixed with or spread over the 

 finer marine sediments. 



Having shown that the southern limit of the present 

 Waimea Plain at one time coincided with the nortbern limit of 

 the Nelson Triassic basin, our inquiry naturally leads us to an 

 investigation of the character of tlie old Palieozoic land-surface 

 whose erosion yielded the material for the Trias formed on its 

 shores. 



We have already found that the coarser sandstones and 

 conglomerates are principally composed of ciiorites, granites, 

 felsites, and quartzose material, none of which occurs in situ 

 as a land-surface in the vicinity of Nelson. The nearest 

 granite-area lies to the north-west along the flanks of Mount 

 Arthur range and lower course of the Motueka River. In that 



• An interesting petrological description by Dr. Marshall of material 

 from the upper granite conglomerate will be found in Article XXXVI. 



