TRANSACTIONS OF SECTION J. 479 



mountain railways worked by special systems of traction are, 

 in the opinion of experienced engineers, no longer a question of 

 doubt, but are methods of locating correct both in theory and 

 in practice ; and, as the construction of railways will yearly 

 extend into districts more and more inaccessible by nature of 

 the country to be passed over, so must special means be 

 adopted by the engineer to surmount such difficulties, and 

 reduce the cost of construction and maintenance to a point 

 which will make such mountain lines not only possible to 

 construct and maintain, but also financially successful. Ex- 

 perience seems to show that the solution of this problem is 

 the application of steep-grade inclines on mountain railways. 



4. Drift-material of Ncto Zealand Beaches, and their Effect 

 on Harbour-ivorks and Bivers. 



By C. Napiee Bell. 



The question of what becomes of the material denuded from 

 the mountains by the frosts and rains is nowhere so forcibly 

 brought to mind as in New Zealand, where, from the 

 peculiar structure of the main mountains, composed of hard 

 metamorphic slates and sandstones, shivered and fractured in 

 every direction, the quantity of boulders and gravel brought by 

 the rivers from the mountains to the sea is not exceeded in any 

 part of the world. The mountains are crumbling away with 

 amazing rapidity, and the rivers and torrents are burdened 

 with a vast amount of work in removing this material to its 

 resting-place in the sea. Figuratively speaking its resting- 

 place is the sea, but actually the materials from the mountains 

 find no rest there : arrived at the sea-beach they have before 

 them a long and toilsome journey, far more restless and weary- 

 ing than that just accomplished down the river-beds. 



The subject of the travel of sea-beaches has been exten- 

 sively discussed, and there is a considerable amount of litera- 

 ture on the subject in the Proceedings of the Institute of Civil 

 Engineers ; but the travel of the New Zealand beaches, espe- 

 cially those of the South Island, shows this peculiarity in 

 which they differ from those of most other countries which 

 have been brought under notice : that the travel is invariably in 

 one direction, and that is towards the north. If this in the 

 meantime be taken for granted, one is confronted with the 

 question of what becomes of the vast quantities of sand, gravel, 

 and boulders which are yearly brought by the rivers from the 

 crumbling mountains to the sea. 



