A. Milward, Esq., 0” the Motion of a Lava-Stream. 49 
paper. In fig. 1, I have attempted to shew, by black and 
dotted lines, the first and second state of things at the foot 
of the névé steeps. 
I am disposed therefore to conclude that the difference of 
mechanical pressure in connection with the greater and 
and smaller ridges is not sufficiently effective to warrant us 
in supposing that the compression caused in throwing up the 
summer ridge is the cause of the ice being then more compact. 
So that we cannot from this suppose structural bands of 
porous and compact ice to have any existence worthy of con- 
sideration. The difference of consistency will depend solely 
on the different degree of saturation in the summer and win- 
ter névé. 
But to return to our observations on the lava-stream. 
As there are in the motion of a glacier peculiarities not com- 
mon to other viscous bodies, and resulting from the varying 
action of heat at points below ordinary temperatures, so in 
a lava-stream are these characteristics no less striking, de- 
rived from the action of heat at higher temperatures. Indeed, 
so remarkable are the effects of this action, that few persons 
would be prepared at first sight to identify the masses of 
cinders which terminate one of these streams with the glow- 
ing current that issues so smoothly and rapidly from the in- 
terior of the mountain. The chief characteristics of lava ap- 
pear to be the intense heat of the mass as it issues from the 
interior, and its very low conducting power, which causes it 
to retain for a long period its viscous nature. It is said also, 
that the cohesion of its particles is not very great. 
The heat of the mass on its first appearance, allows the 
opportunity of rapid atmospheric action, favoured by the 
escape of gas, and the slowness with which the cooling action 
passes into the interior. The surface is in this way en- 
eumbered by a scum or slag which gradually passes into 
scoriz, until at the lower part of the stream a complete chaos 
of cinders is presented to view. At no great distance from 
the source it appears to be a mass of broken fragments and 
pinnacles when seen at hand; but from a more distant and 
elevated point, a general impression of diverging streams is 
clearly produced. Occasionally a fragment at the termina- 
VOL. XLVII. NO. XCY.—JAN, 1850. D 
