373 



these lake basins, and the relation of the interior lakes to the Sounds on the 

 West Coast. 



The section, the general position of which is shown on the map~by the 

 dotted line A to B, has been carried over a higher range of mountains than 

 actually occurs in this line, for the purpose of showing the manner in which 

 the glaciers have excavated the valleys, and rather i-epresents a former than 

 the present condition of that particular part of the range. The dark patches 

 on the map represent a few only of the moraines that are shown on the original 

 map which is in the Otago Museum, and which gives the full details of the Pleis- 

 tocene geology of this interesting district. 



The Wakatipu lake, which is fifty-two miles in length and two to three 

 miles in width, lies, in its upper part, between the Schistose rocks on the east, 

 and the upper Palseozoic rocks on the west, so that it marks the junction of two 

 formations. Its surface is 1070 feet above the sea level, which is exceeded by 

 its depth, for it has been found by soundings to vary from 1170 to 1296 feet, 

 the bottom of the lake being nearly level from side to side, and from end to 

 end. The waters of the lake, at the present time, escape over a rocky fall at 

 Frankton, which is almost the middle of its eastern side, but from the lower 

 end of the lake, at Kingston, a broad valley can be traced to the south, joining 

 that of the Mataura river, which, at first sight, appears to have been the 

 former outlet. The lake is fringed by terraces showing the gradual shrinking 

 of its area, as the level of its outfall has been lowered. The only apparent 

 barriers, in the direction of the Mataura valley, is a great moraine accumula- 

 tion at Kingston, elevated 270 feet above the level of the lake ; but on 

 following down the Mataura river it is found to run over a rocky channel, and 

 to cut its way through a gorge at an altitude of 700 feet above the sea, so that 

 even were the Kingston barrier removed, the lake would not be completely 

 drained in that direction. The lake is therefore contained in a rock basin, and 

 not formed by the simple damming up of a valley. 



On the western side of the range, within a distance of thirty to forty miles, 

 we have, on the other hand, a series of arms of the sea occupying exactly similar 

 excavations, frequently 1800 feet beneath the sea level. McKerrow lake is an 

 example of one of these, the exit of which has been barred by coast drift 

 covering a moraine like that barring the lower end of the Wakatipu lake, 

 at Kingston. The outlet of McKerrow lake is by the Kaduku river, 

 which is a tidal river, so that the surface of the lake is at the sea level ; yet 

 its waters, which are quite fresh, have a depth of at least 470 feet. Milford 

 Sound, which is also shown on the map, twelve miles further south, has a 

 depth, at its upper part, of 1270 feet, but across its entrance the depth is only 

 130 feet, while the mountains surrounding it rise to 6000 and 9000 feet. 



All the valleys on both slopes of the range are occupied by glacier 

 moraines, and although it is only in the higher cluster of mountains that we 

 now find glaciers to exist, there is no want of evidence of their former greater 

 extension. 



The section will explain the operation of glaciers in excavating valleys : 

 a a represents an area of the mountain top, which is above the altitude of per- 

 petual congelation, and from which therefore the snow deposited can only 

 escape by assuming the form of ice, descending by its weight as a glacier b 

 through the valleys to the point at which it melts, owing to the increased 

 temperature counterbalancing the supply of ice. At this point it deposits its 

 moraine or rubbish heaps c, and moraines found further down the valleys are 

 sure indications of the glacier having had formerly a greater extent. At the 

 point where the ice descends from the plateau a to the glacier b, it is generally 

 an abrupt fall, known as the " ice cascade," and it is at this point that the 

 chief amount of erosion takes place, by which the valleys are eaten back into 



