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XXIII. Addendum to Contributions to the Mineralogy of Nova 

 Scotia. By Professor How *. 



III. On Borates in Gypsum and Anhydrite. 



MY attention has been drawn by Principal Dawson to some 

 particulars mentioned in the paper named above which 

 I shall be glad to state ; at the same time I am enabled to give 

 some interesting facts he has kindly communicated, and take 

 the opportunity of giving an analysis of gypsum bearing on one 

 of them, and of adding a few remarks on other points. 



In the first place I have inadvertently named Cape Canseau 

 as a locality of plaster, I should have said the Gut of Canseau. 

 The former is some thirty miles south of the latter; and, as 

 stated by Dr. Dawson, a large part of the peninsula, terminating 

 at Cape Canseau, is occupied by white fine-grained gneiss with 

 veins and masses of granite ; there is also much mica-slate and 

 dark-coloured slate ; it is in fact quite destitute of gypsum. The 

 Gut of Canseau is the narrow strait between Nova Scotia proper 

 and Cape Breton ; and on the Cape-Breton side is situated Plas- 

 ter Cove, where the beds referred to are seen. They are thus 

 described in a passage of ( Acadian Geology/ which I am sorry to 

 have overlooked at the time when it would have been of great 

 service to me. " About two-thirds of the thickness of the bed 

 consist of crystalline anhydrite, and the remaining third of very 

 fine-grained common gypsum. The anhydrite prevails in the 

 lower part of the bed, the common gypsum in the upper ; but 

 the greater part of the bed consists of an intimate mixture 

 of both substances, the common gypsum forming a base in 

 which minute crystals of anhydrite are scattered, and bands 

 in which anhydrite prevails alternating with others in which 

 common gypsum predominates/'' In a subsequent page (283) 

 an explanation is given of the mode in which the gypsum and 

 gypseous marl may have been formed from sea-water containing 

 sulphuric acid in varying quantities, and the fact stated that 

 anhydrite must have been deposited with the gypsum, and that 

 it seems difficult to account for its production, unless it may 

 have been formed by acid vapours and scattered over the bed of 

 the sea. Dr. Dawson does not think the existence of salt proves 

 anything as to the origin of the gypsum, as, under any probable 

 hypothesis, the rock must have been formed in the sea, and, as 

 the marls and sandstones seem to indicate, in limited and pro- 

 bably shallow basins. 



In speaking of ordinary sea-water not containing the boracic 

 acid found in the borates in plaster here, I might have referred 

 to the interesting discovery of the acid in limited portions of the 

 * Communicated by the Author. 



