812 STUDIES FOR STUDENTS 



as having observed ripple marks while diving at depths of 60 and 

 70 feet. 1 



In 1883, the year following the publication of Hunt's earliest 

 paper cited above, there appeared three important essays on ripple 

 marks: one by De Candolle on " Rides formees a la surface du 

 sable depose au fond de l'eau et autres phenomenes analogues"; 

 another by Forel on "Les rides de fond etudiees dans le lac Leman"; 

 and a third by Darwin "On the Formation of Ripple-Mark in 

 Sand." De Candolle produced ripple marks artificially by experi- 

 menting, not only with sand and various substances in powdered 

 form covered by water, but also with liquids of varying viscosity, 

 covered with water and other liquids. 2 Regarding sand or powder 

 mixed with water as a viscous substance, he concluded from his 

 experiments that "when viscous material in contact with a fluid 

 less viscous than itself is subjected to oscillatory or intermittent 

 friction, resulting either from a movement of the covering fluid or 

 from a movement of the viscous mass itself with respect to the 

 covering fluid, (1) the surface of the viscous substance is ridged 

 perpendicularly to the direction of friction, and (2) the interval 

 between the ridges is directly proportional to the amplitude of the 

 friction-producing movement." That ripple marks depend on 

 simple friction alone, and not on any change of level in the covering 

 liquid, such as occurs during wave action, De Candolle proved by 

 an experiment with a rotating disk submerged in a tank of water. 

 After submerging the disk and mixing an insoluble powder in the 

 water, the apparatus was left until the powder settled on the disk 

 and floor of the tank as an even film, and the water came to rest. 

 An oscillatory rotary movement then applied to the disk caused 

 radiating ripples to form upon it, while no ripples formed on the 

 stationary bottom, and the surface of the water remained quiescent. 

 The author concludes that the formation of ripples in sand, whether 

 under currents of air or under water currents, is identical in origin 

 with the formation of water ripples under moving air. If the cur- 



1 A. R. Hunt, "Facts Observed by Lieut. Damant, R.N., at the Sea-Bottom," 

 Geol. Mag., N.S., V (1908), 31-33. 



2 C. de Candolle, "Rides formees a la surface du sable depose au fond de l'eau et 

 autres phenomenes analogues," Archives des sciences physiques et naturelles, 3 e Ser., 

 IX (1883), 241-78. 



