When a compound glacier is long, the different moraines, lateral and 
medial, sometimes become blended in their progress downwards, and 
spread out into a broad sheet; and if the ice were to disappear, we 
should. find the whole bottom of the valley at this part covered with a 
confused assemblage of fragments of rock. This is — ties oc- 
ee met with in Scotland. 
_ The materials of moraines are not stratified, but huddled sels in 
Seaton The fragments are generally somewhat rounded by mutual 
attrition, but some are angular. They may be distinguishedfrom the 
banks of gravel formed at the margin of lakes by their internal strue- 
ture, a the difference of level ase their — aaa and also by 
their form 
We are not ee sure of the precise aie of eal moraines, 
but the terms employed by Agassiz (digues ow remparts) lead us to 
suppose that they form long mounds with rounded sides. Like the 
others, they are not stratified internally; but, from the manner of their 
formation, they contain more finely triturated matter, namely, clay, 
_ sand, and small gravel. Agassiz seldom gives precise measurements ; 
but he mentions one terminal moraine, (that of Viesch,) which is thirty 
feet high, and much more in breadth. Glaciers sometimes advance for 
a term of years, and then retreat for another term. When a glacier 
is retreating, it forms a new terminal moraine every year, and when it 
again advances, it pushes the more recent ones before it till the whole 
are blended into one mass. Now, if the disappearance of the glaciers 
took place gradually, as it seems most reasonable to suppose, we ought 
to find in the lower end of some of our valleys a series of little trans- 
verse mounds, like x, 9, in figure 5, below. 
Lateral ‘mata increase in size towards the lower end of the val- 
ley, and for an obvious reason: The fragments which fall at the head 
of the valley are slowly carried downwards by the glacier in its course, 
and they are joined in their progress by those which fall from the rocks 
in the lower part of the valley. Blocks which fall into the nevé or 
granular snow high up, sink into it and disappear for a time ; but it is 
curious, that except those which tumble into crevasses and reach the 
bottom, they all afterwards rise to the surface. Agassiz thinks, that 
the internal dilatation. which makes the glacier travel downwards, also 
operates upwards, and carries all included masses to the surface. Itis 
certain that an enclosed boulder is never seen in the terminal section of 
a glacier, where the composition of the mass can be best observed. In 
i also of the sides of the glacier travelling faster than 
the middle, and of its breadth generally diminishing towards its lower 
end, it very often happens that the blocks of medial mealies ien ee 
way to the sides and join the lateral ones. whi td a Ne BEE 
Vol. x11, No, 2.—Jan.-March, 1842. 45 
