714 SEC. 16. GEOLOGY AND MINING. 



fine particles are sorted or not into thin or thicker bands according as the 

 screw is moved in an irregular or regular manner, just as occurs when a 

 current moves with varying velocity. The arrangement of the materials thus 

 produced is in all respects similar to what is so often seen in certain beds of 

 stratified rocks. 



3298. Microscopical Sections of Shells and Bocks. 



H. C. Sorby. 



These are prepared by grinding down one side to a perfectly flat and 

 smooth surface, which is then fixed to a glass with Canada balsam. After 

 this, the other side is ground down, first with emery and at last on a very 

 hard piece of water of Ayr stone, so as to leave a thin portion of the rock in 

 a perfectly undisturbed condition attached to the glass, with a smooth and 

 almost polished surface. According to the nature of the rock, the thickness 

 of such sections should vary from about T i w to -j-jy^th of an inch. Thin 

 glass is then mounted over the whole with Canada balsam. As examples of 

 rocks presenting special difficulties, attention may be drawn to the sections 

 of soft chalk, and of slate and mica schist, cut perpendicularly to the cleavage 

 or foliation. 



3299. Lithographed Plates, illustrating the Microscop- 

 ical Structure of Limestones. H. C. Sorby. 



These show structure due to larger or smaller fragments of organic bodies 

 or grains of sand, and to the more or less complete development of crystals 

 formed either during or after the deposition of rock. 



3300. Working Model, illustrating the Movement of 



Waves in forming ripple marks. H. C. Sorby. 



The model shows the movement of the particles at the surface and at the 

 bottom of a wave which has advanced from deep to shallow water, so as to 

 give rise to ripple marks. At the surface the water moves nearly in circles, 

 which in the model is represented by the white discs attached to arms con- 

 nected with each alternate wheel. At the bottom the water moves forwards 

 and backwards, drifting the sand in the line of the movement of the wave 

 when its crest is passing, and backwards when the trough is passing. In the 

 model this movement is produced by the action of small eccentric wheels on 

 pieces of brass fixed at one end and carrying white discs at the other. 



33OOa. Specimens relative to the contributor's studies of 

 synthetical and experimental Geology. 



1. Minerals formed at about 400 by overheated water (1860). 



2. Product of the reactions of vapours. 



3. Contemporaneous minerals, produced by the action of hot 

 springs (1858 to 1876). 



4. Transformation of terrestrial rock into meteoric rock (1866). 



5. Imitation, by experiment made with native magneti-polar 

 platina (1875). 



6. Experiments upon the possibility of capillary infiltration 

 through the pores of rocks, notwithstanding the resistance of a 

 high steam pressure (1861). 



7. Experiments upon the schistose properties of rocks, geo- 

 logical deductions (1860 to- 1876). M. Daubree, Paris. 



