158 Scientific Proceedings, Royal Dublin Society. 



on smooth surfaces will not think it improbable that on the sur- 

 face of fine sand we should find it simulating organic form. 



My failure in obtaining the 0. antiqua artificially may have 

 been due to the texture of sand employed, to its degree of satura- 

 tion, or, possibly, to the nature of the matter dissolved in the 

 water. Thus, it might not be amiss to try experiments on the 

 freezing of sea- water in mud or fine sand ; and a sand made of 

 the silurian slate itself, crushed to dust, commends itself, perhaps, 

 as going towards realizing past conditions. 



The subsequent preservation of these marks in the mud during 

 thawing and drying may be perfect, and conditions necessary for 

 their continued preservation, as rock-marks are no harder to con- 

 ceive than the conditions which have preserved to us the rain- 

 marks so perfectly that we can pronounce, it is said, on the direc- 

 tion of the wind prevailing during the shower. 



We have only to suppose alternations of high and low water — 

 the silt-laden water creeping very quietly over mud flats which, 

 frozen during exposure, were again thawed and dried before the 

 incoming water deposited a fresh covering. 



It is noteworthy that the grosser spicules appearing on the 

 surface of frozen mud leave, so far as I have observed, no impress. 

 They are, in fact, formed merely in surface-water. 



It was hoped at first that evidence might be obtained from a 

 comparison of the angles made by the bifurcating branches of 

 the frost-marks with the angles easily measurable on the silurian 

 slate. But as the crystallographic directions were found to be 

 completely disguised in the first case, the comparison was futile. 



In bringing these observations to the notice of the Society, I 

 hope it will be understood that I no more than venture a sugges- 

 tion, worthy, it is thought, of further elucidation, and not to be 

 lightly dismissed. Even if, on further consideration, it be 

 deemed improbable, it is perhaps not without interest, and, pos- 

 sibly, not without important bearings in other directions to point 

 out that the fragile and beautiful frost flowers, fleeting as they 

 are, can leave an impress of a nature capable of being preserved 

 through an eternity of time. 



