1864.] HAAST EXCAVATION OF LAKE-BASINS. 131 



The sequence of changes effected by the glaciers is then traced, 

 and attention is called to the fact that they soon formed for them- 

 selves channels in the platean-like mountains, and that, running in 

 these channels, they gradually became narrower and deeper ; the 

 specific gravity of the ice became greater, and consequently its scoop- 

 ing and triturating power much more considerable ; thus, a con- 

 stantly increasing quantity of detritus would be furnished for the 

 formation of moraines. The loose Tertiary strata lying in the course 

 of the advancing glaciers would soon be removed, unless protected 

 by favourable circumstances. The existing depressions were widened 

 and made straighter by the glaciers, and their reentering angles 

 were either entirely removed or worn into roches moutonnees. 



Dr. Haast next gives a sketch of the formation of the terminal 

 moraines, and states that the water issuing from the glacier, being 

 charged with finely triturated matter, would deposit it amongst the 

 coarser material, so as to make the moraine impermeable, and that, 

 the detrital matter being in excess of what could be transported to 

 lower regions, the bed of the outlet would be raised. The result is 

 stated as follows : — " From that moment the formation and scoop- 

 ing out of the rock-basin begins. Hitherto the ice of the glacier, 

 having a sliding action, by gravitation, and pressure from the de- 

 scending masses above, had only to overcome the impediment of the 

 asperities of its bed, bottom, and sides. Now, the glacier in ad- 

 vancing would find an impediment in the form of a very compact 

 mass before it, which, like rocks in situ, had to be ground down 

 before it could make a new channel for the collected water. But 

 this water could not accumulate below the ice, but would be forced 

 up into the fissures of the glacier, until it reached the level of the 

 lowest point in the moraine. The ice, being impelled downwards by 

 the vis a tergo, would be pressed most heavily against the rocky 

 bottom of its bed, where it had to ascend over the moraine, and 

 would now find it a much easier task to plough out a deeper bed for 

 the accommodation of the masses of ice pressed on it from behind. 

 Moreover the finely triturated glacial mud would be forced into the 

 body of the ice by the enormous pressure, and would assist in scoop- 

 ing out a hoUow. Thus many causes would combine to give addi- 

 tional scooping-power to the glacier at the spot where the terminal 

 moraines — now consolidated into one large mass — would impede the 

 advancing of the ice, as well as the outflow of its former outlet." 



All these operations were stated to be still going on in a minor 

 degree ; and the author illustrated his views by giving a description 

 of the existing Tasman glacier, which was said to furnish a very 

 close parallel to the requirements of his theory. 



Pursuing the sequence of events during the glacial period, the 

 author stated that, finally, the glaciers began their retreat, from 

 various causes, especially the sinking of the country, the diminution 

 of the plateau-like neves-fields, through the ridge-making effects of 

 the glaciers, and the wearing away of the heights by atmospheric 

 influences. The rock-basin which had been excavated by the sta- 

 tionary glacier would now be exposed, and a lake would be formed 



