Marshall. — Fmina of ihc Hainixhn Beds. 239 



submerged at an earlier date as the sea margin gradually advanced west- 

 wards. Actually the Wharekuri beds contain 18-7 per cent, of the species 

 that are found in the Hampden beds, and this is a larger percentage than is 

 found in any other of the beds in the Oamaru district. 



Classification of the Oamaru System. 



These comparisons between the Hampden fauna and that of other 

 localities within the Oamaru area is of special interest in view of criticisms 

 that have lately been made by Thomson,* and of classifications that have 

 been proposed by Park.f and of statements which have been made by 

 Morgan. { 



In various publications I have insisted that the series of rocks that rest 

 on the Hokonui formation, or on rocks that are older than these, belong 

 to one period of continuous deposition. The u|)per limit of this formation 

 has been placed by me as certainly not below the base of the Wanganui 

 rocks, and perhaps as high as the upper limit of this formation. This 

 whole system of rocks I have called the Oamaru system. 



This suggestion to classify all the younger rocks in a single system has 

 been constantly opposed by Park, who has written, " To the young geologist 

 there is always something attractive and alluring about a Cretaceo-Eocene 

 succession." Since 1904 he has been pointing to one horizon after another 

 as obviously the plane of division between the Cretaceous and the Tertiary, 

 but in each case he has been forced to withdraw from his position. His 

 latest statement, after being forced to retreat from his position of 1912, 

 is : "A settlement can only be reached by a detailed geological survey 

 of the middle Waipara and Weka Pass districts. "§ This is the result after 

 fifteen years of effort to find a plane of disjunction in a small area where 

 continuous sections are remarkably clear in stream-valleys running generally 

 at right angles to the strike. 



Morgan, in discussing this proposal to classify all these younger rocks 

 in one system, writes : '' This proposal has not been fruitful in any respect 

 save in the promotion of discussion and in the temporary thickening of the 

 cloud of confusion involving an admittedly difficult problem." It is only 

 necessary to add that it has stimulated research in such a way that it is 

 now definitely known that the planes that were previously thought to be 

 breaks between different geological formations are merely stratigraphical 

 planes in a series of continuous deposition. 



Thomson, on the other hand, agrees with the proposal to regard all the 

 sediments above the Hokonui system up to and including the Wanganui 

 system as a single formation " which were called by Marshall and his col- 

 leagues the younger rock-series of New Zealand, and named by Marshall 

 the Oamaru system. Previous classifications had not brought out the 

 close diastrophic relationship of this group of rocks, and in this respect 

 the paper in question marked a great advance." 



Thomson objects to the use of the name " Oamaru " for this rock- 

 system. He lays stress on the fact that the name had been previously used 

 for a rock-system in New Zealand, and he says also that the strata are not 



* J. A. Thomson, Trans. N.Z. Inst., vol. 48, pp. 28-40, 191(5 ; also vol. 49, pp. 397-413, 

 1917. 



t J. Park, N.Z. Geol. Surv. Bull. No. 20, 1918. 



% P. G. Morgan, 10th Ann. Rep. N.Z. Geol. Surv.. Pari. Paper C.-2b, p. 28, 1916. 



§ J. Pab,k, Trans. N.Z. Inst., vol. 49, p. 393, 1917. 



