141 



sometimes forming thick beds, and large rounded masses. It is 

 white or grey, and crystalline, lamellar, or granular. It contains oc- 

 casionally bituminous matter. It does not occur in veins, but is tra- 

 versed by veins ol" gypsum. 



The gypsum beds are entirely destitute of fossils. 



Many salt springs rise from the lower carboniferous and gypsi- 

 ferous rocks, but rock-salt has not been discovered. 



The lower carboniferous limestones are usually filled with shells 

 and corals ; but there are some limestone beds which are granular 

 and crystalline without fossils. These beds agree with those of gyp- 

 sum in their structure, and in containing bituminous mattex*. 



4th, The origin of the gypsum. The author concludes by stating 

 his opinion, that the gypsum beds cannot have been formed in situ ; 

 but that they may have originated from the action of sulphuric acid, 

 conveyed by the rivers into estuaries of small extent, the waters of 

 which, from the abundance of marine fossils, must have been rich in 

 carbonate of lime. The acid may, he thinks, have been derived 

 from the oxidation of iron pyrites, which is very abundant in the 

 older formations. That free acid may have been present, he consi- 

 ders probable, from the blanched appearance of certain sands and 

 clays adjoining the beds, while the neighbouring beds are strongly 

 coloured by iron. Moreover, as might be expected, on the hypo- 

 thesis of the decomposition of pyrites, oxide of iron is very abundant, 

 both colouring the rocks very strongly, and in the form of large beds 

 of brown hematite. The oxidation of the pyrites may have been 

 promoted by internal heat, of the action of which on the older rocks 

 there is abundant proof. There is also good evidence that the beds 

 of gypsum were deposited in trough-shaped hollows of small extent ; 

 and if we suppose the supply of acid to be intermittent, this would 

 account for the alternation of beds of gypsum, and of shell limestone. 



The author considers the regular bedding of the anhydi'ite and its 

 association with unaltered rocks, to preclude the idea of its being 

 gypsum altered by heat in situ ; and thinks it may have been first 

 altered by heat, and subsequently deposited at the bottom of the sea, 

 although its great purity is not favourable to this hypothesis. 



There was exhibited, in illustration of this paper, a lai-ge collec- 

 tion of specimens, presented by the author to the Society. 



2. On the mode of occurrence of Gypsum in Nova Scotia, and 

 on its probable origin. By the Same. 



In this paper, the author, after a general description of the geolo- 



