52 A. Milward. Esq., on the Motion of a Lava-Stream. 
part moving in layers over the under, which was in contact 
with the cold, or o/d lava, as we may call it. These layers were 
by no means parallel with the course of the stream, or with 
the surface, but assumed undulating forms evidently caused 
by the variation of declivity, and the obstacles at the bottom. 
Little portions of scorize often described a curved path as 
they rolled over with the layers of the stream. The fact of 
the layers moving at different rates was made evident to the 
eye by the existence of incipient lines of scoriz partially 
covering the red lava. On the surface a similar differ- 
ential motion was still more apparent near the origin. It has 
been already remarked, that the lava was perfectly red and 
glowing, as it emerged from the hole in the cold lava,* but it 
gradually assumed a darker appearance as its surface became 
encumbered with slag. This did not come on uniformly, and 
much sooner at the sides than towards the centre of the stream. 
Through a length of about five or six feet, and a breadth of 
nine or ten inches, the central part exhibited only slight 
parallel longitudinal markings, consisting of ribbons of slag 
alternating with the hot lava; and thus appeared to indi- 
cate the movement of bands or lamine of lava passing one 
another at different rates, and so tearing as it were these 
shreds of slag. ‘Towards the sides the slag became more 
and more continuous, but was honeycombed, as it were, with 
openings, caused perhaps by the escape of gas; and here the 
red lava was exposed. These openings also served to make 
manifest the fact, that the central parts moved with greater 
rapidity ; for by noticing the relative positions of certain of 
them when they approximated to a line pointing obliquely up 
the stream, this line of direction would gradually be seen to 
become transverse, and then to point down the stream at the 
same time that it discontinued to be a straigh¢ line.t 
* T have spoken of the lava as cold, but this is only relatively correct, for 
near the rising stream, and particularly behind it, the black surface was too hot 
to be stood upon with any comfort, and everywhere the lava surface was more 
or less warm. 
+ I very much regret that the fact of my forming one of a large, though 
pleasant, party, and the near approach of evening, prevented my making such 
exact observations as to the peculiar appearance of the surface of the lava as I 
