264 
THE TERTIARY VOLCANOES 
BOOK VIII 
V-. 
fissure, which runs for about 20 miles in a north-east direction, 
the cones amount to some hundreds in number. 
The cones consist generally of slags, cinders, and blocks 
of lava. They are on the whole not quite circular but oblong, 
their major axis coinciding with the line of the chasm on 
which they have been piled up, as along the marvellous line 
of the Laki fissure. In many places they are exceedingly 
irregular in form, changes in the direction of outflow of lava or 
of escape of steam having caused the cones partially to efface 
each other. 
As regards their size, the cones present a wide range. 
Some of them are only a few yards in diameter, others several 
hundred yards. Generally they are comparatively low mounds. 
On a fissure hardly 30 feet long, Mr. Thoroddsen found a 
row of twelve small cones built exactly like those of largest 
size, but with craters less than three feet in diameter. On 
the Laki fissure some are only a couple of yards high ; the 
majority are much less than 50 yards in height, and hardly 
one is as much as 100 yards. 1 2 And yet these little monti- 
cules, as Mr. Helland remarks, represent the pipes from 
which milliards of cubic metres of lava have issued. While 
other European volcanoes form conspicuous features in the 
landscape, the Icelandic volcanoes of the Laki district, from 
which the vastest floods of lava have issued in modern times, 
are so low that they might escape notice unless they were 
actually sought for." 
As they have generally arisen along lines of fissure, the 
cones are, for the most part, grouped in rows. The hundreds 
of cones that mark the line of the Laki fissure present an 
extraordinary picture of volcanic energy of this type. In 
other instances the cones occur in groups, though this 
distribution may have arisen from the irregular uprise of 
scattered vents along a series of parallel fissures. Thus to the 
north-east of Laki a series of old cones entirely surrounded by 
the lavas of 1783 lie in groups, the most northerly of which 
consists of about 100 exceedingly small craters that have sent 
out streams of lava towards the ET.N.E. 3 
It would appear from Mr. Helland’s observations that the 
same fissure has sometimes been made use of at more than one 
1 Mr. Thoroddsen, however, states that there are about 100 ranging between 
20 and 100 metres in height. 
2 Op. cit. p. 27. 
3 Op. cit. p. 25. The great lava-fields of Iceland are likewise dotted over 
with secondary craters or “ hornitos ” which have no direct connection with the 
magma below, hut arise from local causes affecting the outflowing lava. They 
are grouped in hundreds over a small space. 
