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Transactions. 



The downthrown area is partly covered by the harbour of Port 

 Nicholson, which occupies the seaward portion of the drowned valley of 

 the Hutt River, and also portions of some smaller valleys which appear 

 to have been tributaries of the now dismembered Hutt. The date of 

 subsidence, whether before or after the beginning of the present cycle in 

 the high-standing block, has not been deduced with certainty from the 

 outlines of the partly submerged Miramar Peninsula and adjoining ridges. 

 Mature slopes are now the rule, and younger slopes, if they have existed, 

 are submerged. The deep water that is to be found over the greater 

 part of the harbour (fig. 5) is an indication either of a great amount of 

 sinking of the submerged block, or, on the other hand, of the recent date 



of the subsidence. Enormous quantities 

 of waste must have been delivered to the 

 harbour by the streams which enter it 

 along the Wellington fault and have cut 

 their gorges in the post-faulting period. 

 Since tidal currents are insignificant to 

 prevent silting, the range being only 3 ft. 

 to 4 ft., the existing freedom from shoals 

 must therefore be taken as an indication 

 of great initial depth and large initial 

 capacity of the basin. The Hutt River, 

 entering at the northern end, has already 

 built an extensive delta of sand and gravel, 

 but the enormous loads of waste tipped 

 over the fault-scarp by the Kaiwarra and 

 the Ngahauranga have not been revealed 

 even by the uplift of 5 ft. which took 

 place in 1855 (see p. 259). Fig. 5, which 

 is a rough contour-map of the harbour- 

 floor, gives an idea of the manner in 



Depths in fathoms below L.W.b. ° ... . , 



Data from the "New Zealand which sediment is being evenly spread 

 Nautical Almanac," 1910. out as a flat layer in the deep water 



of the harbour. It will be noted that the 

 hallowest water is near the entrance, where a dredge is at work lifting 

 sand and shells. The shallow water at the entrance appeals to be due 

 to the accumulation of waste broken by wave-action on the outer coast. 



The material furnished by marine erosion on the outer coast has 

 completely blocked one former entrance to the harbour. A bar of sand, 

 or tombolo,* has converted a former island into a peninsula (Miramar 

 Peninsula), and divided a former channel into two bays (Lyall Bay and 

 Evans Bay). A good example is here afforded of the manner in which 

 a coast-line is straightened (regularized) by wave-action, as described by 

 Davisf and by de Martonne.J 



Fig. .">.— Port Nicholson. 



* See F. P. Gulliver. "Shore-line Topography," Proc. Am. Ac. of Arts and Sci., 

 vol. 34, No. 8, 1899, p. 1^9. 



f " The Outline of Cape Cod," Proc. Am. Ac. of Arts and Sci., 1896 ; reprinted in 

 Geogr. Essays, 1909, p. < 90. 



% " Geographie physique," p. 685 ; Paris, 1909. 



