506 
lets and grinding down tlie rugosities of bottom and sides. Thus 
the scooping and ridge making action of ice and water began. If this 
bo the case, the area of the snow-fields, as the mountains began 
to become more and more eaten into by the eroding action of the 
descending ice and the wearing away of the heights by atmospheric 
influences and sharp ridges and peaks were more and more formed, 
must have been rapidly diminishing; and in the same measure as 
the valleys were scooped out , the glaciers must have retreated from 
the coast towards the centre of the mountains and their extent di- 
minished. Thus we have the most simple and natural explanation 
for the fact, that the glaciers of New Zealand since the pleistocene 
period have been more and more retreating into the deep alpine 
valleys to their present limits; and we need not suppose, that the 
pleistocene glaciers, although generally larger than the present ones, 
attained such an enormous length , as the distance of their terminal 
moraines seems to indicate. Judging, however, from the structure 
of the Hounds on the West-side of the mountains, and that of the 
Lake districts on the East-side , it seems probable that the opposite 
sides of the mountain range have besides undergone repeated and 
alternate oscillations to the extent of at least 1000 feet in either 
direction from a nominal point; and that the western district being 
at present near to the period of greatest depression the re-elevation 
of the land to the other extreme would be also sufficient to extend 
again the glaciers to farther limits. 
From the present features of the New Zealand Alps we can 
easily imagine what enormous masses of rock must have been des- 
troyed in course of time by the combined action of atmospheric 
influences, of ice and of water. We need only look upon the im- 
mense extent of drift, partly glacial, and partly alluvial throughout 
the Alps, and as far as the borders of the sea, to know what has 
become of them. The rocks desintegrated into boulders shingle sand 
and mud , and the colossal moraines of the glaciers have furnished 
the material for the drift-formation, which on the foot of the moun- 
tains forms extensive plains, filling the valleys up to a height of 
more than 1000 feet, and which extends from valley to valley across 
