440 Transactions. — Geology. 



clay and brecciated limestones that extend in all directions 

 underneath the sea, the limestones, and the plain, and is really 

 the basin in which all the artesian-bearing beds have been 

 deposited. The most sudden slopes in the plain are between 

 Roy's Hill and Pakipaki, where in a distance of eight miles there 

 is a fall from 166 - 4 ft. to 32*39 ft., or nearly 17 ft. to the mile. 

 and between Roy's Hill and Omahu Pa, where in a distance of 

 six miles the slope is 103 ft., or 27" 17 ft. to the mile. Between 

 Roy's Hill and Hastings the slope averages about 16 ft. to 

 the mile, so that the Hastings slope in reality represents the 

 middle of an immense fanlike area with its pivot or centre 

 at Roy's Hill and the fan spreading from Omahu Pa to Paki- 

 paki with a gradual tilt towards the latter place. If we keep 

 in view the general slope of the plain as shown here, it will 

 be evident that the filling-in of the plain was rather by 

 way of the old course of the Ngaruroro, and that the filling- 

 in was greatly assisted by the Tutaekuri, which came down 

 from the Moteo and joined the Ngaruroro in the vicinity of 

 Omahu. The Tukituki rendered no help in the formation 

 of the western part of the Heretaunga Plain, but its burden 

 of shingle, deposited in a fan-formation from Te Mata, diverted 

 the course of the Ngaruroro, turning it northward when in 

 vicinity of the old mill at Havelock, and this was the general 

 direction of the latter river until the year 1867. when it was 

 diverted into its present bed. If we follow to their sources 

 the three rivers that pass across portions of the Heretaunga 

 Plain, it will be found that only the Tukituki had its origin of a 

 chainlike lake formation from the time its waters reached the 

 Ruataniwha. The Ngaruroro and the Tutaekuri rush from the 

 mountains through a deep gut without the trace of a valley 

 formation, and the high angle of slope will be seen by reference 

 to a map showing the Ngaruroro from its rise at about 1,800 ft. 

 above sea-level to the sea, a distance of sixty miles. The basin- 

 area of each of the three rivers is as follows : Tukituki, 937 

 square miles; Ngaruroro, 836 square miles; and the Tutaekuri. 

 326 square miles : or a total of 2,099 square miles. 



The latter rivers run mainly through a shingle and light sandy 

 country, covered here and there with a yet lighter pumice sand. 

 The deep gorge-like bed of each river shows how rapidly the 

 rocks arc wearing away, and this process is greatly assisted by 

 the high angle of inclination of the upper part of each river, which 

 enables even the heaviest timber to be carried in time of Hood. 

 Thus the Ngaruroro from its source at the hack of the Kaweka 

 Mountains as far as Omahu has a fall of 10 ft. per mile, hut 

 between Omahu and Pakowhai the fall is suddenly reduced 

 to about 8 ft. per mile, and for the remainer of its course the 



