176 THE PRINCIPLES TNVOLYED m EOCK-WEATIIERINa 



that when felclspathie fragments were submitted to artificial 

 trituration in a revolving cylinder containing water, a decompo- 

 sition was effected whereby the alkalies were liberated in very 

 appreciable amounts. lie found further that the principal 

 product of mutual attrition of feldspar fragments in water was 

 not sand, but an impalpable mud (Union) . This mud was of 

 such tenuity as to remain for many days in suspension, and 

 on desiccation became so hard as to be broken only with 

 the aid of a hammer, resembling in many respects the argil lites 

 of the coal measures, but differing in that it carried a high 

 percentage of alkalies. Granitic rocks thus treated yielded 

 angular fragments of quartz and very minute shreds of mica, 

 while the feldspars ultimately quite disappeared in the form 

 of the impalpable mud above mentioned. It was noted that 

 after the quarts^ose particles had reached a certain degree of 

 fineness further diminution in the size ceased, owing to the 

 buoyant action of the water, which in the form of a thin film 

 between adjacent particles acted as a cushion and prevented 

 actual contact to the extent necessary for mutual abrasion. It 

 is to similar action on the part of sea-water that Shaler^ would 

 attribute the lasting qualities of the sand grains upon sea 

 beaches. Indeed the conditions of Daubree's experiments as 

 a whole were not so different from those existing in nature that 

 one need hesitate, as it seems to the writer, to conclude similar 

 action, both chemical and physical, may be going on wherever 

 abrasion takes place in the presence of continual moisture, as in 

 the bed of a river or glacier. 



The hammering action of waves upon the sea-coast exerts a 

 powerful erosive action, particularly upon particles of rock of 



measured rate of speed, so that the actual distance travelled by any of the 

 particles during a given time could be readily calculated. The product of 

 this disintegration, even when carried to the condition of fine silt, was always 

 sharply angular. His experiments further showed that when feldspathic 

 fragments were thus treated, there was always a certain amount of decom- 

 position, whereby salts of potash were liberated; in one instance, when 3 

 kilogrammes of feldspar were revolved for 192 hours in iron cylinders con- 

 taining 5 litres of water, 2.72 kilogrammes of finely comminuted mud were 

 obtained, and in solution in the water, 12.6 grammes of potash, or 2.52 

 grammes per litre. The presence of carbonic acid in the water increased 

 the amount of potash. When the feldspar was triturated dry and then 

 treated with water, no such solvent action could be detected. — Geologie Ex- 

 perimentale, p. 268. 



1 Bull. Geo! Soe. of America, Vol. V, p. 208. 



