104: Transactions. 



Drainage of the Southern Area. 



The Opuatia River, with its upper east-flowing tributaries, cuts across 

 the strike of the rocks of the Mesozoic older-mass where these are exposed 

 in its upper course. This indifference to the strike of the folded rocks can 

 be explained by supposing these streams to be superposed consequents. 

 On account of having had their courses shortened by coast-recession, the 

 streams flowing west from the watershed are shorter than those to the east. 

 Those flowing north-west, having maturely dissected the fault-scarp facing 

 the Waikato River, are obviously streams consequent on the deformation. 

 Their courses are short and their drainage areas small. 



From Port Waikato the main watershed runs in a south-easterly 

 direction for forty miles or more. 



The Maretai Stream, flowing north into the Waikato River, has cut its 

 way down to grade along what is believed to be a fault-line, on the west 

 side of which the beds of the older-mass are strongly downfaulted, the scarp 

 on the upthrow (or eastern) side being immaturely dissected. This fault 

 probably extends a long distance south-west. A sunken outlier of the 

 younger-mass at Newdick's, on the western side of the stream-valley, 

 appears to owe its position to the effect of the faulting along this line. 



Most of the streams flowing east or west are graded, and the Okahu and 

 Maretai Streams, flowing north-west, are similarly graded in their lower 

 courses. The Waikawau Stream, seven miles south from the Waikato 

 River, is graded for some two miles of its lower course. Its middle course 

 is between the high vertical walls of its limestone gorge, which soon widens 

 out to a broad valley, the floor of which is covered by flood-plain and delta 

 deposits. 



The Kawa Stream, still farther south, has a comparatively bottle-necked 

 outlet to the sea. In its middle course it flows across extensive flood-plain 

 swamps, which cover a broad depression, believed to have originated in the 

 foldings and dislocations of the beds of the older-mass and younger-mass 

 alike ; which are made evident in the coast sections from the Waikawau 

 Stream along the Waiwiri Beach to the Kawa Stream. Solution may have 

 played its part, as in the Waikawau and upper Huruwai valleys. The 

 writer's first impression was that it represented a gigantic sinkhole. 



The Older-mass of the Southern Area. 



It has been pointed out above that the southern area consists strati- 

 graphically of a younger-mass unconformably overlying an older-mass. 

 The writer considers that the sediments of the older-mass are folded in 

 fairly symmetrical waves measuring four miles from crest to crest, the strike 

 of the axes of the folds being about 30° west of north. The limbs of the 

 folds have an average dip of about 30° and a maximum of 45°. The 

 average is that of thirty-two determinations in different localities. These 

 sediments are therefore not less than 7,000 ft. thick in those portions above 

 sea-level. The conclusion as to the symmetry of the waves is deduced 

 from the evidence of strike and dip of the beds along the Waikato River, 

 as well as from those along the Opuatia and Huruwai Streams and the 

 coast sections. 



In the deepest part of the anticline, which is exposed in a good section 

 at the South Waikato Head, the lowest beds visible are the belemnite 

 shales — a fine, slightly calcareous mudstone containing some thin, light- 

 coloured, highly calcareous bands. In these, but more conspicuously in 



