162 MR GOODCHILD. 
This is nearly what has happened in the case of the 
Stalactitic agates, of which those from a locality near Cupar 
in Fife afford very beautiful examples. In these agates the 
ingress of solutions tending to deposit Chalcedony has taken 
place rather more freely than usual, and mainly from the 
upper surface of the cavity. As a consequence, the material 
has slowly gathered, first into drops, and then, as the quan- 
tity increased concurrently with a partial coagulation of the 
material, they have steadily lengthened out, and pendant 
stalactites of very beautiful forms have resulted. Some of the 
finest examples of these come from Firoe; and the Edinburgh 
Museum can boast of specimens of the kind from both there 
and Fife which are surpassed by none for both their beauty 
and the instructive illustration they afford of the process 
under description. I have lately got some fine examples from 
the lower of the two upper lavas near the Giant’s Causeway. 
In some few cases the stalactites have lengthened until 
their free ends have nearly reached to the floor of the cavity. 
In a few others the chalcedonic material has accumulated 
faster than it has coagulated, and “stalagmites ” have resulted. 
Such cases, however, are very rare. 
It has occasionally happened that the ingress of chalce- 
donic silica has continued without interruption until the 
entire cavity not occupied by the stalactites has been filled. 
In that case, what has happened may be readily understood 
by taking notice of the effects of putting one’s hand, with the 
fingers stretched slightly apart, into a strong solution of soap, 
and then withdrawing it with the finger-ends downward. 
It will be noticed that the soap solution clings in greatest 
quantity to the hand at these points where the fingers come 
into closest contact, and least so where they are widest 
asunder. Surface Tension or Capillarity comes most power- 
fully into action where two adjacent surfaces come most 
nearly into contact, hence the result mentioned. Bearing 
that illustration in mind, one can readily understand how it 
happens in the case of a stalactitic agate that the largest 
quantity of the chalcedonic solution is deposited at those 
points where the bases of the stalactites are nearest to each 
other. It will further be clear from the same that the con- 
tinuance of the process must end with quite filling up the 
