Mineral Evolution. hi 



Ice-ferns form on shallow pools of water in the 

 street gutters or elsewhere during- a slight frost, and 

 look like feathers floating on the surface. As they 

 are similar in appearance and in mode of formation 

 to the frost-ferns on window panes, a description of 

 the latter shall serve for both. The facts regarding 

 frost-ferns are as follows : — 



(a) On steaming the inside of a window pane during 

 a hard frost, a crystal appears at various points, and 

 grows with the rapidity of lightning by the accretion 

 of other crystals. In every case, a central mid-rib 

 first darts forward in a direction obviously dependent 

 upon the depth of moisture in the area around it ; 

 but keeping pace with it, branches shoot from its 

 sides, and from these again sub-branches, until the 

 whole intervening area is traceried with an artistic 

 net-work of ice-needles resembling the venation of 

 a leaf. 



(b) If several mid-ribs shoot out from one centre 

 or root, each leaf parts company with the others. 



(c) If two fronds approach from separate starting 

 points they mutually attract, curve round and merely 

 touch points, or lock each other in an embrace. 



(d) Fronds growing downwards from the upper 

 edge of the pane attract lower ones growing upwards. 



(e) Two fronds budding from the lower edge or 

 from a similar pole, with well-defined points and 

 beautiful outlines, have been observed on nearing to 

 repel and shatter each other's extremities. 



(/) No ordinary objects seem to influence the 



