226 Miss C. A. Raisin. On certain Structures formed 



slightly curved,* perhaps about J inch in diameter, and | inch at 

 thickest. They differed from the ' frost ferns,' in a much greater 

 simplicity of structure, being more like little bunches of grass 

 arranged along a stem than those exquisite and intricate fabrics of 

 the ice-world. They reminded me sometimes of the groups of 

 actinolite crystals in certain crystalline schists, as for instance at the 

 St. Gothard. These actinolites, on examination under the microscope, 

 prove to be not pure crystals, but much interspersed with granules 

 of pre-existing minerals. It occurred to me that the probable 

 reason for the formation of these ice structures was the impediment 

 offered by the small grains in the mud to the growth of tiny crystals. 

 Only here and there, where circumstances were exceptionally favour- 

 able, a crystal larger than usual would be developed, which, as it 

 advanced, gathered to itself other crystalline molecules. Thus 

 would be started a bunch of coarse crystals, springing from a common 

 centre, growing more easily in the direction of the axis of the 

 rhombohedron, just as in the case of frost ferns, but they would be 

 simpler, coarser, and arrested by the impediments, instead of delicately 

 flexured by the almost imperceptible inequalities of the glass. 



" I obtained on a later morning, strong confirmation of this view. 

 Heavy rain fell all through the preceding day, followed by a clear 

 night, with a ground-frost. In many places the pavements had 

 been washed very clean. On the clean paving stones I saw, not 

 unfrequently, early the next morning, fairly delicate frost ferns 

 (though not equal to those on glass). Where the surface had been 

 a little dirty, the forms were less intricate and coarser; in some 

 rather dirty places the old types could be seen. 



" Postscript. What is written here was my impression at the time, 

 but I have since doubted whether the crystals were not ' muddier' 

 than the part around. It was not possible to examine the pavement 

 very closely ; also I noticed on a later occasion that the trampling of 

 the film of mud (prior to freezing), which produced a kind of con- 

 centration in an irregular network of wavy lines or bands, appeared 

 to have something to do with the formation of the flowers." 



This note suggests that analogous processes may be traced in 

 schists, like those of the St. Gothard, and the mode of formation of 

 certain crystals in schists has been described in papers already pub- 

 lished.f On this point, however, it is needless to enlarge, as we may 

 hope to receive more results, since Professor Bonney has communi- 

 cated a paper dealing with this subject to the Geological Society. 



* Similar forms were noticed on certain days in the winter, 1896-7. 



f " On a Secondary Development of Biotite and of Hornblende in Crystalline 

 Schists from the Binnenthal," by Professor T. Gr. Bonney, ' Quart. Journ. Geol. 

 Soc.,' 1893, vol. 49, p. 104. Also " On some Schistose Greenstones, &c.," by the 

 same author, ibid., p. 94. 



