462 Transactions. 



Alluvium and Sandstone. 



Alluvium. — Over the low-lying parts of the district the alluvial 

 deposits of the Taieri and Tokomairiro Plains overlie the foliated 

 schist ; their thickness must be considerable, but it could not be 

 determined in this district. Captain Hutton considers the allu- 

 vium of these plains as of Pliocene age. 



Sandstone. — At several parts of the district a brown sand- 

 stone is found above the limestone. It outcrops clearly in two 

 places — at J. Gray's farm, and on the western hill which juts 

 out to form Waihola Gorge ; elsewhere the sandstone reveals its 

 presence only by loose boulders on the surface. Professor Park* 

 considers that this is an original formation, deposited in shallow 

 water on top in succession to the limestone. He says, " From 

 the upper surface of the limestone to the basalt cap there is an 

 interval of 120 ft. to 150 ft., apparently occupied by a yellowish- 

 brown sandstone, the character and disposition of which could 

 not be ascertained on account of its outcrop being obscured by 

 a heavy slope deposit of black earth mixed with sand. In the 

 Oamaru and Weka Pass districts, where the sequence of Lower 

 Tertiary strata is very complete and characteristic, the Oamaru 

 and Weka Pass calcareous sandstones, which, as we have seen, 

 are the time-equivalents of the Millburn limestone, are followed 

 quite conformably by the Hutchison quarry or Mount Brown 

 beds, which consist of yellowish-brown calcareous sandstone con- 

 taining a rich assemblage of marine forms. This overlying series 

 is so closely associated with the Oamaru series that it cannot be 

 regarded as a separate formation, but only as the closing horizon 

 of the Oamaru series itself. Until something more definite is 

 ascertained about the sandstone lying above the limestone 

 on the Horse-shoe Estate, it may be correlated with the Hut- 

 chison quarry horizon of the Oamaru formation." 



A careful examination of the district has led me to differ from 

 the above views of Professor Park, and has forced me to believe 

 that the sandstone was not laid down as sandstone, but that it 

 is a secondary deposit, formed, where conditions were favourable, 

 from the weathering of the subjacent limestone. When the 

 limestone weathered away, the quartz-grains in it were left be- 

 hind and formed sands, which were afterwards cemented together 

 by iron-oxide to form a compact sandstone. The following are 

 the reasons which have induced me to differ from Professor 

 Park's views, and to advocate the theory of a secondary origin : — 



1. In this sandstone we do not find several features which 

 we ought to find in a normal sandstone deposited in shallows by 



*Park, Trans. N.Z. Inst. (1902), vol. xxxv, p. 396. 



