340 Transactions. 



Age and Fonnaticn of the ''Grey Mads."— Owing to the great range 

 of the majority of Oanmruian IMoUusca, the list of fossils so far collected 

 from the " grey marls " is insufficient in itself to prove whether the beds 

 are Lower, Middle, or Upjjer Oamaruian. If, hoM^ever, a correlation with 

 the " grey marls " of tlie Weka Pass district is admitted, it is necessary 

 to consider them Middle Oamaruian or Ototaran, since in that locality 

 they are followed by the Mount Brown beds, the uppermost limestone 

 band of which is Awamoan, and the middle or main band Hutchinsonian 

 on the evidence of the rich brachiopod fauna. It is, indeed, possible that 

 part of the Mount Brown beds is Ototaran, so that the " grey marls " 

 can hardly be younger than that stage. 



According to diastrophic considerations, the presence of thick beds of 

 mudstone following limestone in such a series as the Notocene is evidence 

 of a gradual sea-retreat, causing renewed denudation of the thick soil- 

 mantles accumulated on the peneplained land which formed the coasts 

 of the middle Notocene seas. If this sea-retreat is in the main due to 

 movements of the hydrosphere, then the correlation of the " grey marls " 

 throughout North Canterbury and Marlborough appears well based. The 

 uniform lithological cliaracters of the upper part of the Amuri limestone, 

 the phosphatic greensand, the Weka Pass stone, and the " grey marls " 

 throughout these areas supports the belief that the changes of the 

 deposits are mainly due to movements of the hydrosphere. The chief 

 difficulty lies in the conception of gradual emergence in the district 

 north of the Rakaia Biver at the ver}^ time (Ototaran) when there 

 was greatest submergence south of that river. Perliaps the true 

 explanation is that the whole of the Ototaran is comprised within the 

 Mount Brown beds, which were formed in a ]>eriod of renewed depression. 

 This would involve the consideration of the '" grev marls " as Waiarekan, 

 but there would still be the dilficidty of the gradual emergence in the 

 northern district at the time of a marine transgression in the southern 

 area, so that there seems no escape from an hypothesis of warping in 

 minor diastrophic districts, to some extent luasking the effects of 

 movements of the hydrosphere. 



The Great Marlborough Conglomerate and Awatere Beds. 



The conglomerate which closes the Notocene series in the greater part of 

 the Middle Clarence Valley (Plate XXIX, fig. 1), in common with similar 

 conglomerates in other parts of Marlborough, was termed by McKay the 

 " great post-Miocene conglomerate," from the belief that certain Tertiary 

 sandstones which occnr as boulders within it were of Miocene age. The 

 Miocene of Plector and McKay's classification comprised the beds now 

 classed as Awamoan and Waitotaran, the latter stage being later than 

 Miocene, so that the name used for the conglomerate is unsuitable. 

 Although McKay considered that the conglomerate contained boulders 

 of sandstones of the Awatere series, which ranges from Awamoan to Wai- 

 totaran, there is reason to believe that in the Clarence Valley there are 

 no boulders of rocks younger than Oamaruian in the conglomerate, which 

 itself appears to be an Oamaruian rock. It is preferable, therefore, to 

 use a local name for the rocks, and I suggested in 1913 the alteration of 

 McKay's name to " great IMarlborough conglomerate." Under the latter 

 name Cotton in 1911 described fully the nature of the conglomerate and 

 discussed its relationship to the underlying formations in the Mead and 

 Dee Gorges, and foi' these localities 1 have little to add to his account, 

 which is freely quoted below. 



