364 



imbedded in the solid crystalline gypsum are common near 

 the surface of the deposit. Some of them are 3 to 4 inches 

 (7-5 to 10 m.) in length and are perfectly terminated and 

 easily separated. Satinspar, the fibrous variety, is rare at 

 Hillsborough. 



For the origin of the gypsum deposits of New Brunswick 

 and Nova Scotia, Dawson proposed a conversion of cal- 

 careous beds by means of sulphuric acid, the acid being 

 derived from igneous rocks and active volcanoes. This 

 theory is an improbable one since there are ,at least in New 

 Brunswick, no extensive bodies of igneous rocks present in 

 the neighborhood of the gypsum deposits. Furthermore 

 the gypsum often exhibits a series of approximately 

 parallel lines of a darker color. These lines represent planes 

 of easy cleavage and are thin films of calcium carbonate. 

 Assuming an origin as proposed by Dawson it would indeed 

 seem strange that sulphuric acid should convert practically 

 the whole mass to gypsum and leave a series of films of 

 calcium carbonate unattacked. 



The field evidence obtained by the writer indicates a 

 transformation of the anhydrite into gypsum. Evidence 

 of this is especially abundant at Hillsborough. The gypsum 

 rests upon a bottom of anhydrite and reaches a maximum 

 thickness of perhaps 125 feet (38 m.). The hydration of the 

 anhydrite can be observed in many places, taking place 

 in either of two ways, namely: — ■ (i) Hydration is uniform 

 from the surface towards the centre of the mass and the 

 increase in volume caused by the process breaks and 

 shatters the outer layers. (2) Hydration starts along 

 some crack or fissure which becomes filled by gypsum. 

 The force exerted by the gypsum during its formation, 

 causes the anhydrite to split into a network of fissures 

 along which hydration proceeds and eventually converts the 

 whole mass into gypsum. 



It is, however, not likely that the calcium sulphate was 

 originally deposited in the form of anhydrite. The 

 physical chemistry of anhydrite has never been understood. 

 Van't Hoff determined thermodynamically, that anhydrite 

 is deposited in a saturated sodium chloride solution at 36° C. 

 Actuall3^ to the writer's knowledge, this has never been 

 experimentally verified. The claims of geologists for the 

 deposition of calcium sulphate as anhydrite are principally 

 based upon the fact that anhydrite is found in nature, and 

 upon the experiments of Van't Hoff. The first is an idea 



