Thomson. — Geology of Middle Waipara and. Weka Pass District. 333 



Thomson (1916) discussed the age and mode of origin of the Amuri 

 limestone throughout North Canterbury and Marlborough, quoting fossils 

 from it at Amuri Bluff and the Trelissick Basin (discovered by Speight and 

 Thomson) which proved the fossil-horizons to be Tertiary. As these occurred 

 near the top of the limestone, which was always underlain by Cretaceous 

 rocks, lie concluded that it was in itself a Cretaceo-Tertiary rock — Cretaceous 

 at the base and Tertiary at the* top. He pointed out that the appearances 

 of unconformity between the Amuri limestone and Weka Pass stone were 

 not present where the base of the latter rock was not glauconitic, and 

 concluded, therefore, that it was a purely local phenomenon, and not 

 indicative of a non-sequence of any extent. He suggested that the Amuri 

 limestone was in large part a chemical deposit, its silica content and its 

 poverty in fossils becoming then easily explicable. 



In 1917 Woods described the Cretaceous fossils of North Canterbury 

 and east Marlborovigh in the collections of the Geological Survey. He 

 found that rocks of two ages were represented, those of east Marlborough, 

 north of Amuri Bluff, developed especially in the Clar.nce Valley (c/. 

 Thomson, 1919) and the Awatere Valley, being of Lower Utatur (approxi- 

 mately Albian) age, and those of Amuri Bluff, Waipara and Weka Pass, 

 and the Malvern Hills being Upper Senonian. In the Middle Waipara and 

 Weka Pass district ail the fossils came from the Ostrea bed and the '' saurian 

 beds," and in most cases were poorly preserved. 



Thomson (1917) proposed the Ideal terms " Clarentian " and " Piri- 

 pauan "" for the two groups of Cretaceous rocks correlated by Woods as 

 " Albian " and " Upper Senonian " respectively, basing them on the rock- 

 sequences below the Amuri limestone of the Clarence Valley and Amuri 

 Bluff'. He criticized the grouping of all the younger rocks of New Zealand 

 by Marshall as a strictly conformable series deposited during a single cycle 

 of depression and elevation, the period of maximum depression being every- 

 where contemporaneous, on the grounds that the Amuri and Oamaru lime- 

 stones were of different ages and that unconformities are present in some 

 districts. He rejected also Marshall's use of the name " Oamaru " for a 

 system to include all the younger rocks, both on grounds of priority and 

 because only a small part of them were developed at Oamaru, but admitted 

 the necessity of an inclusive name for them in view of their diastrophic 

 unity as more or less accordant rocks, deposited in a period of relative 

 diastrophic inactivity between two periods of major diastrophic activity, 

 and proposed the name " Notocene." The references to the Waipara and 

 Weka Pass district were mostly to questions of correlation, but a summary 

 of the succession from the coal-beds at the base to the Weka Pass stone 

 was given with a view to showing the thinness of the beds between the 

 highest known Piripauan and the base of the Amuri limestone. The tilted 

 gravels unconformably overlying the marine succession in the Kowhai River 

 were also briefly discussed. 



Park (1917) suggested that not only was the tuff-bed recorded by 

 Thomson and Speight in the Amuri limestone of the Trelissick Basin 

 Oamaruian, but the whole of the Aiiiuri limestone throughout New Zealand 

 should be placed in the Tertiary, and an unconformity looked for below 

 it, probably between the " saurian beds " i nd the overlying greensands, in 

 which latter Haast had recorded a Recent brach'opod in the Middle Waipara. 



In 1917, also, Trechmann described Cretaceous Gasteropoda from New 

 Zealand, mostly from the Selwyn Rapids, but one species from the Oalrea 

 bed of the Waipara Gorge was included. 



Speight and Wild (1918) gave a careful and very detailed description of 

 the contact between the Amuri limestone and the Weka Pass stone, not 



