564 
BASALTES. 
by far the most numerous. It has been noticed by 
every one who has examined basaltic columns, that 
they are for the most part formed of a number of 
pieces, nearly equal in size, which rest one upon 
the other, and which are immediately detected by 
the line of separation. On removing any of these 
pieces from the main column, they are almost al- 
ways found with one face convex and the other con- 
cave. 
The basaltes of which the causeway is composed is 
of a blackish colour, and hard enough to strike fire, 
imperfectly, with steel. It is of a close texture, and 
disturbs the magnetic needle. 
When any cavities are perceived in the basaltic 
pillars, it is more generally towards the top than 
elsewhere. Indeed it has been said, that the upper 
joint of each pillar, where it can be ascertained 
with any certainty, is always rudely formed and 
cellular. The gross pillars also in the capes and 
mountains frequently abound in holes through all 
their parts, which sometimes contain fine clay, and 
other apparently foreign bodies ; and the irregular 
basaltes, beginning where the pillars cease, or lying 
over them, is in general extremely honey-combed, 
containing in its cells crystals of zeolite, little mor- 
sels of fine brown clay, sometimes very pure steatite, 
and in a few instances bits of agate. 
From the iron ore found intermixed with the 
basaltes, and the vast beds of red ochre which sepa- 
rate the ranges of columns at different heights, 
M. Pictet very reasonably supposes that iron in the 
