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On the Motion of a Lawva-Stream, observed on the Side of 
Mount Vesuvius, 27th April 1849. By A. MILWARD, Esq. 
Communicated by the Author. 
Some observations on a Mud-Slide in Malta, published in 
the Philosophical Journal at the commencement of the pre- 
sent year, having been read with some interest, it has occurred 
to me that an account of some peculiarities connected with 
the motion of lava-streams, which have since come under my 
notice, may not be altogether unacceptable. 
Professor Forbes has already drawn attention to this sub- 
ject; and were it not that accident appears to have present- 
ed me with a more favourable opportunity than he seems to 
have enjoyed, these remarks would be superfluous from me. 
The chief interest they can possess, will consist probably in 
the light they may throw on the phenomena of the motion of 
viscous fluids ;—and here I have the opportunity of present- 
ing some interesting evidence of the tearing action pro- 
duced by the difference of motion in the various parts which 
make up the breadth of the stream. Before, however, I pro- 
ceed to this description, I would wish to make afewremarks on 
Professor Forbes’s Fifteenth Letter on Glaciers. In a paper 
on Glacier Dirt-Bands, read before the British Association at 
Swansea, and afterwards published in this Journal, I ventured 
to put forth three inquiries, all of which seem to be answered 
by Professor Forbes in the affirmative. It appears, 1st, That, 
toa slight extent, structural bands of porous and compact 
ice are, if I mistake not, supposed to exist in the upper part 
of the glacier, consequent upon the mechanical pressure and 
compression which forms the ridges; but, nevertheless, this 
seems to be only a secondary phenomenon. 2d/y, That there 
are waves or ridges, arising from similar causes to those 
which originate the ridges in a mud-slide; and, 3dly, That 
the saturation of the névé at the foot of the upper slopes, 
resulting in gushes of wetice and snow, is the cause of these 
simultaneous phenomena. 
