HOLWELL CAVERN. 17 
although this earth is found in many arragonites, there 
are at least an equal number without it. The main differ- 
ence between arragonite and common-carbonate of lime, 
consists in its greater hardness and difference of erystalli- 
zation—ın fact, it is altogether a different arrangement of 
molecules. This arragonite contains no other substance 
than carbonate of lime, with the exception of now and 
then a small proportion of oxide of iron, which occasionally 
tinges it, giving it a peach blossom, pale red, or yellow 
colour. 
So far Ihave given a description of this fissure in the 
limestone rock, or rather in the united rocks of the Iime- 
stone and clay state. I now come to the cause of these 
erystalline formations.. During several distant periods of 
my life, I have visited this cave, feeling assured that I 
should sooner or later learn some new principle from an 
examination into its interesting erystallizations.. I have 
ever considered that in one sense it is better to follow 
nature blindfold than art with both eyes open; and very 
many years since I felt convinced that the formation and 
constant growth of the crystalline matter which lined the 
roof of this cavern, was caused by some peculiar upward 
attraction; and reasoning more upon the subject, I felt 
assured it must be electric attraction. Sir Humphry Davy, 
in pursuing the train of his magnificent discoveries, had 
found that while all acids were attracted to the positive pole 
of a voltaie battery, in like manner all alkalies, earths, 
and inflammable substances, were directed to the negative 
pole. His experiments were carried on mostly with very 
powerful batteries, whose action soon ceased ; and although 
splendid in their results, were perfectly incapable of pro- 
dueing those more durable effects which are shown by a 
feeble, but long-continued, electrica action—such as 
1851, PART II. {6} 
