THE SUBSIDENCE OF TARTICLES IN LIQUIDS. 175 



or less colloid, or, if not soluble as a colloid, having different degrees of attraction towards the 

 water. When some of these are slowly evaporated at low temperatures, the resulting solid is very 

 bulky at first, colloidal in appearance, shrinking enormously on drying, and after being dried 

 behaving very differently towards water. The effects of fieezing and tliawiiig are also suggestive. 



In short, there are many indications that clays (and perhaps other similar comiiounds) under 

 certain conditions in water enter into new clieinical combinations with the water, forming com- 

 ^)ounds having some colloidal characters, which compounds are stable only under a very limited 

 range of conditions, but which are nevertheless of vast importance in the economy of nature. My 

 own experiments have extended to a relatively small number of substances, but chemical literature 

 of recent years mentions colloidal forms of various metallic oxides, and my experiments may 

 illustrate but narrow phases of much wider-reaching phenomena. 



Geological sugf>estions other than those already noted are sufficiently abundant, and have 

 occurred all along the line of the investigation : suggestions pertaining to the segregation of 

 veins, the X)bases of lamination in certain slates, tlie hardening of comminuted corals and shells 

 into liinestones, the effect of the alkaline salts evolved bi the decomposition of rocks, the action 

 and effects of alternately hot and cold waters on rocks and in veins — these and many other possi- 

 ble relations. The experiments were begun with very limited objects, but. as they have gone on 

 and widened with time they have suggested very many possibilities. 



