Oct. 1847.] 273 



Near the entrance of Wallace Harbor is a bed of gypsum, whose relations 

 are as follow, in descending order : 



1. Reddish clay or shale, not well seen. 



2. Grey limestone with fossil shells. Its fissures and the cavities of the 



shells filled with selenitic gypsum. 



3. White granular gypsum ; thickness about 12 feet. 



4. Reddish clay and shales. 



5. Grey sandstone, with calamites and trunks of coniferous trees. 

 The dip of these beds is S. S. W. 20. 



The above are the best illustrations which, on looking over my notes, I can 

 find of the stratification of gypsum. There is, however, one circumstance 

 worthy of notice, in addition, as it aids in generalizing from such facts. It is 

 the rude lamination or layering observed in many masses of gypsum. This 

 always coincides with the plans of stratification, where the latter can be ob- 

 served, and is often produced by the presence of thin layers of clay, marl, or 

 limestone. In beds whose associated rocks cannot be seen, this lamination is 

 often observable, and affords an evidence of stratification, which may some- 

 times be farther confirmed by a comparison with the nearest visible beds of 

 other rocks. In some cases also, this layering affords proofs of disturbances. 

 An instance of this is the enormous bed of gypsum, called White's or the Big 

 Plaster Rock, on the banks of the Shubenacadie. The indications of the 

 singularly contorted laminae of this bed are confirmed by the vertical position 

 of some associated thin beds of marl and limestone. 



Anhydrite very frequently accompanies the common gypsum. In some 

 cases, as at White's quarry, and the bend of the Shubenacadie, it forms the 

 lower parts of beds, which above consist of hydrous gypsum. In other instances, 

 as at the estuary of the Avon and the St. Croix river, it constitutes the mass of 

 greafbeds, which are, however, in the immediate vicinity of the beds of the com- 

 mon variety. At the East river of Pictou, it occurs in large balls, included in 

 a thick bed of hydrous gypsum. The anhydrite is sometimes also dissemi- 

 nated in grains, through some parts of the beds of gypsum, which are quarried ; 

 and this mixed rock, as well as the purer anhydrite, is called hard plaster or 

 shark-stone, by the quarrymen. Anhydrite has not been observed to be con- 

 nected with any igneous or metamorphosed rocks. In the only instance which 

 I have observed of the occurrence of gypsum in rocks altered by heat, the 

 gypsum is hydrous. 



The gypsum of this province is nearly always crystalline. In the great beds, 

 whether of common gypsum or anhydrite, the structure is always foliated or 

 granular ; sometimes large grained, in other cases so fine as to appear compact 

 or chalky. The finer grained varieties often contain groups of larger crystals. 

 In the true veins, occupying fissures in the sandstones, limestones, and gypsum 

 beds themselves, the structure is invariably fibrous. Little rounded kernels of 

 gypsum, sometimes occurring in sandstones, &c, are foliated. 



The crystalline structure, and great comparative purity of gypsum, show that 

 it is a chemical, not a mechanical deposit. Its constant association with the 

 limestones of the carboniferous system, containing marine fossils, (Terebratula 

 Productus, Orthoceras, Corals, &c.) prove that it was deposited in the sea; and 



