58 Shingle on the East Coasts of New Zealand. 



this is almost at right angles to the beach, no waves of 

 any size can be formed to carry the shingle along it. The 

 advance of shingle beyond this point is probably due to 

 the cutting-out action which takes place afc times, the finer 

 material being drawn under the water-line by certain 

 waves. On this point more information is required. 



16. The largest stones, or pebbles, which composed the 

 shingle seen by the author in New Zealand seldom measured 

 more than 6 inches by 4 or 5 inches by 3 inches. Several 

 stones, measuring a third or so more each way, were seen 

 near the mouth of the Rivei\Waitaki. The usual size of 

 those on the beach was, however, much less than above 

 stated ; occasionally, near Napier, it was little more than 

 that of coarse sand. These stones have, evidently, from their 

 rounded appearance, before being thrown on to the beach, 

 been subjected to the action of water in a former age, 

 and are now found embedded in earth. They are chiefly 

 derived from the rivers already mentioned, down which 

 they are carried during freshets. 



17. A further source of supply is in the mountains in 

 which the Canterbury rivers have their source, where there 

 are "long slopes from 500 to 1000 feet high, as regular as the 

 slopes of a railway embankment, and formed entirely of 

 clay -slates, broken up to the size of road metal ; the stone 

 lies at an exact angle of repose, and if a shovelful were taken 

 from the foot the movement would extend to the top of the 

 slope. . . . Even where the rocks are not actually 

 broken up, they are so easily disintegrated that every small 

 stream forms a large fan of shingle when it reaches the 

 valley. During floods the streams cut deep gulches through 

 these fans, carrying the shingle away into the main river." 

 The inclination of the bed of the River Waitaki " is between 

 30 and 40 feet per mile, while that which the bed of a river 

 of the same size would take if no new shingle were brought 

 into it would not be greater than 3 or 4 feet per mile."* 

 The cliffs along the coast, particularly on the South Island, 

 are said also to furnish a large portion of the supply of 

 shingle. 



. 18. The banks of the rivers are very subject to erosion, 

 and great changes frequently take place in the course of 



* See New Zealand Parliamentary Paper, No. 2, of 1880, pp. 10, 11. 

 Evidence of Mr. Carruthers, Engineer-in-Chief, relative to the Oamaru and 

 Timaru Harbour Works, 



