50 <A. Milward, Esq., on the Motion of a Lava-Stream. 
tion of the stream will be tolerably smooth, and exhibit dis- 
tinct curves and loops. These fragments have much the ap- 
pearance of dried pitch, and the loops rise in masses, and 
have the peculiarity of curling over in some degree. This 
smooth appearance appears to be owing to the thinness of 
the lava at these points—(and perhaps also to some other 
cause), by which it cools more quickly without allowing time 
for the formation of thick scoriz, and the consequent break- 
ing up of the surface. Such examples are to be seen very 
frequently in the lava which in 1819 encroached on the Atrio 
di Cavalli, on the north-west side of the cone of Vesuvius. 
The altered character and appearance of the surface of the 
streams extend to a very varied distance into the interior of 
the mass. Near Torre Annunziata, there is a very good 
section on the railway which shews the remarkable difference 
between the surface and the interior. I find the following 
note of it in my pocket-book. ‘Near Torre Annunziata, the 
railway cuts through a hard and thick stream of lava, appa- 
rently not very ancient, and extending to the sea-shore. It 
is curious to observe the difference between the compact grey 
interior and the brown decomposed surface, which the section 
displays most beautifully. The decomposed part varies in 
thickness from 2 to 6 feet: it is brown and friable, and looks 
like some kinds of hard brown mud crumbling into dust. It 
is partially cultivated, but does not appear old enough to be 
very fertile. The compact lava has cracks and cleavage 
planes passing down vertically or nearly so, more than in any 
inclined direction. 
The lava streams which I had the opportunity of observing, 
formed small portions of a large and broad stream, the result 
of an eruption which occurred in the autumn of last year. 
The lava extends about two miles down the south slope of 
the mountain towards Torre Annunziata, and was still advan- 
cing a short time since. The greater part of the surface at 
the period of my visit was comparatively cold, and presenting 
a rough black surface, but many parts were still in such a 
state as to give off much smoke by day, and exhibit long 
luminous bands at night. In these places, the hot lava 
rising from below was nearer the surface than elsewhere, and 
