GLACIAL PERIOD. 
21 
their final admission, if the ancient glaciers 
had been first formed among the highest moun¬ 
tains, and extended downwards into the plains, 
the largest and highest moraines ought to be 
the most distant, and to be formed of the most 
rounded masses ; whereas the actual condition 
of the detrital accumulations is the reverse, 
the distant materials being widely spread, and 
true moraines being found only in valleys con¬ 
nected with great chains of lofty mountains. 
Again, all these moraines are within one 
another, — the most distant from the glacier 
to which they owe their origin, encircling all 
those which are nearer and nearer to it within 
the same glacial basin. As no glacier could 
reach its farthest moraine without pushing for¬ 
ward all the intervening loose materials, it is 
self-evident that the outer moraines were first 
formed, while those nearer the glacier were 
built up subsequently, in the order in which 
they follow one another from the lower valleys 
to the higher levels at which alone glaciers 
exist at present. Thus we see that the glaciers 
to which these ancient moraines owe their 
origin must have been retreating gradually 
while the moraines were accumulating. But a 
