324 T rdiixaciiuna. 



course of the river. These remarkable alterations are certainly due to 

 interference arising from the glaciers when at their nuiximum or when 

 declining, and how this arose Avill be mentioned later. 



4. Lakes. 



Numerous small lakes and ponds lie in the hollows formed b}- the 

 morainic accumulations between the Potts River and Hakatere. The two 

 largest of these are Lake Ackland (locally known as Lake Emma), at the 

 head of the Pudding Stone Valley, and Lake Tripji (known as Clearwater), 

 which lies near the Potts River. The latter is about two miles in length by 

 about one in breadth. There is a smaller one, called Lake Howard, situated 

 between the two. All of these lakes drain to the Ashburton. To the north 

 of the Ashburton River, near Hakatere Station, are two shallow ponds 

 known as the Maori Lakes, whose water is held back by a barrier of detritus 

 deposited by the aggrading Ashburton River as it crosses the great trans- 

 verse Lake Heron Valley. 



(a.) Lake Heron : its General Features ; with Special Reference to the Spits 



notv forming on its Shores and to the Action of Shore Ice. 



(Plate III, fig. 2.) 



The largest body of water in the district, and the highest lake in Canter- 

 bury, is Lake Heron, which is at an elevation of 2,267 ft. above sea-level, 

 and is situated on the very highest portion of the floor of the transverse 

 valley. It has a most remarkable shape, as it almost encircles an isolated 

 conical hill called the Sugarloaf, which rises to a height of 4,054 ft. The 

 western part of uhe lake has a length from north to south of about five miles, 

 and the southern portion a length from east to Avest of about four miles. 

 Its actual breadth varies from about two miles down to very small dimen- 

 sions where its two encircling arms stretch as narrow creeks behind the 

 Sugarloaf on its north and east. The largest expanse of open water is near 

 the south end. It is rather a shallow lake, but deep alongside the central 

 hill, which carries down its precipitous slopes far below water-level. The 

 shores are fringed in many places with marsh, and are usually without 

 marked features ; but my attention has been drawn to two shingle spits 

 which are found near the south-western corner of the lake (Plate III, fig. 2). 

 These spits are evidently the result of wave-action, without the interference 

 of currents, usually considered to be the principal cause of the formation 

 of such featiues. In this case the}^ are so placed that it seems impossible 

 that currents can have any part in their formation. They occur in a small 

 lake at the end opposite to its outlet, and right at its very extremity. The 

 most powerful wind on the lake is the north-wester, which sweeps down it 

 from the direction of the Rakaia, and sometimes raises waves of such a 

 size as to threaten danger to an ordinary boat. These seem to be the 

 prime factor in the formation of the spits. Starting from a small projection 

 of the shore, the larger spit stretches across a small bay for about 100 yards, 

 and includes a patch of water as in a natural breakwater. The smaller 

 spit is formed under somewhat similar conditions. When the waves are 

 seen coming down the lake they move faster in the deeper water off shore, 

 and gradually swing round where they meet the friction of the shelving 

 bottom. The swing is prolonged till on breaking they are parallel to the 

 margin of the spit ; in other words, the edge of the spit is the tangent to the 

 front of each wave as it breaks. There must, therefore, be some intimate 



