GEOLOGICAL PAPERS. Ill 



DEPOSITION OF GYPSUM THROUGH VOLCANIC AGENCIES. 



Dawson, following Lyell, explained the origin of the gypsum in 

 Nova Scotia as due to an accumulation of these layers of limestone 

 which were later acted upon by sulfuric acid in solution or in vapor 

 produced by volcanic action. The limestone and calcareous matter 

 were thus changed to the sulfate, and gypsum of good quality ac- 

 cumulated in considerable thickness. 



hunt's chemical theory of GYPSUM FORMATION. 



T. Sterry Hunt many years ago proposed a very complex theory 

 of chemical interactions whereby gypsum was formed. The bicarbon- 

 ate of soda acting upon sea-water separated the lime in the form of 

 carbonate, which gave rise to a solution of bicarbonate of magnesia. 

 The action of this solution on tlie sulfates of soda and magnesia 

 formed bicarbonates of these bases and sulfate of lime (gypsum). 



This theory was applied by Logan, in 1863, to explain the origin 

 of the Canadian gypsum by the reaction between solutions of bicar- 

 bonate of lime and water containing sulfate of magnesia, forming the 

 sulfate of lime, or gypsum. 



GYPSUM DEPOSITED IN RIVERS. 



Rivers may in some instances carry high percentages of sulfate 

 of lime, and so deposit gypsum at their mouths or in the basins into 

 which they empty. Lyell cites the river in Sicily known as the La 

 Frume Salso as an example of a river forming such gypsum deposits. 



SECRETION OF GYPSUM BY ANIMALS. 



In the cruise of the "Challenger," M. Buchanan found that the 

 bathybins formed a sulfate of lime deposit. This form is an uni- 

 cellular animal belonging to the lowest group of animal life, the Pro- 

 tozoa, and it forms slimy masses on the floor of the ocean. Many 

 scientists maintain that it is not an animal, but merely a deposition of 

 lime salts in the depths of the ocean. 



GYPSUM FORMED FROM ANHYDRITE. 



Anhydrite, which is the sulfate of lime without water, on taking 

 up two molecules of water becomes gypsum. In this process there 

 is an increase in volume of thirty-three per cent. According to Lap- 

 parent, the force exerted by this change is four times as great as that 

 of water in process of freezing. Such a change on a small scale is 

 found in many places, but in the Harz mountains, according to 

 Gary, the large gypsum deposits are formed from anhydrite through 

 the entrance of water. Near EUrich this change has formed mounds 

 of gypsum in concentric shells fifty-two feet high, often hollow at the 

 interior. The force of the resulting expansion has been sufficient to 

 break crystals of quartz and the dolomite in the layers above. 



