Pakk. — Marine Tertiaries of Otago and Canterbury. 497 



the Mount Brown beds by glauconitic sands, or a band of 

 glauconitie sandstone a few feet thick adhering to the base of 

 the Waitaki Stone, and crowded in places with brachiopods 

 and numerous fine examples of Pscudamussium huttoni, Gir- 

 sotrema broivni, and more rarely Plagiostoma laevigata. 



The calcareous sandstones at Shag Valley, Waikouaiti, 

 and Brighton contain a varied fauna which correlates them 

 with the Mount Brown rather than the Waitaki Stone horizon. 

 At Waikouaiti North Head* they attain a thickness of over 

 350 ft., this great expansion of the lower horizon having 

 apparently taken place at the expense of the Oamaru Stone. 



At Millburn limestone quarry, south of Lake Waihola, the 

 Mount Brown beds are represented by beds of glauconitic 

 sandstone, which pass upward into a compact limestonet 

 about 80 ft. thick. It is probable that the upper part of this 

 limestone and the calcareous sandstones which overlie it are 

 the local representatives of the Waitaki Stone. 



The compact limestone at Millburn is extremely variable in 

 quality along its horizontal extension both going north and 

 south. Passing northward it becomes intercalated with 

 narrow bands of glauconitic sandstone, and attempts to burn 

 the rock for lime at different points have been unsuccessful 

 through the excess of sandy impurity. 



Waihao-Kakahu Beds. 



These generally consist of blue sandy clays and soft bluish- 

 green sandstones which often contain thin layers, or detached 

 lens-shaped masses, of hard calcareous sandstone. Near the 

 old shore-line these rocks sometimes consist of loose pebbly 

 shell beds, or of loose sandy beds and blue clays alternating. 



The molluscous fauna of this horizon is mainly of a littoral 

 character, and it is not a little singular that it contains a 

 number of recent shells that are not often seen in the over- 

 lying Mount Brown beds, and never in the Waitaki Stone. 

 This apparent anomaly is doubtless explained by the circum- 

 stance that the whole series was deposited on a sinking shore- 

 line, and consequently, while the gradually deepening sea- 

 floor favoured the existence of coralline and brachiopod life, 

 it caused the local extinction or migration of the littoral life. 



Where the old coast-line was flat and shelving, the littoral 

 shells would follow the retreating shores westward ; but where 

 the coast-line was bounded by high steep land, as we know 

 was the case for long stretches, the littoral forms would be 

 submerged in uncongenial depths, and compelled to migrate 



"Park, " On the Geology of North Head, Waikouaiti" (Trans. N.Z. 

 Inst., vol. xxxvi., 1903, p. 421). 



t Park, "On the Geology of the Rock Phosphate Deposits of Claren- 

 don, Otago " (Trans. N.Z. Inst., vol. xxxv., 1902, p. 391). 



32— Trans. 



