8 ROYAL SOCIETY OF CANADA 



duction of joints as well, as seen in Plate III, these joint planes deter- 

 mining the forms assumed in weathering as well as the vertical red clay 

 partings by which the beds of plaster are often divided. 



To the features above referred to must be added the fact that 

 at a number of points in and about the quarries, the plaster rock 

 exMbits a markedly concretionary structure, the concretions varying in 

 size from a few inches up to two feet or more, and looking, on the face 

 of exposed bluffs, like the ends of barrels piled one upon another. 

 (See Plate IV, Fig 2). 



"We may now pass on to consider the possible origin of the gypsum 

 deposits (including in this connection both true gypsum and anhy- 

 drite) in relation to theoretical views as to the conditions of such 

 origin, and as indicated by the facts already cited. 



(1) Derivation from limestone through action of free sulphuric 

 acid. This mode of formation, in its application to Acadia, ^\''as 

 strongly advocated by the late Sir William Dawson. It supposes sul- 

 phuric acid to have been formed either as an indirect product of volcanic 

 action, through oxidation of sulphur and sulphurous vapours, or else 

 through the similar oxidation of hydrogen sulphide or metallic sulphides, 

 and, reaching the sea in streams, to have discharged carbonic acid from 

 lijnestones pre-existing there, with formation of calcic sulphate either 

 as gypsum or anhydrite. 



In favour of this view we have the fact that thé gypsums of Albert 

 county are directly and invariably underlaid by limestones, while a con- 

 siderable percentage of calcic carbonate is to be found in deposits of 

 otlierwise pure gypsum. Volcanic activity is also known to have been 

 a marked feature of the Lower Carboniferous age in Acadia, while gyp- 

 sum deposits, undoubtedly thus formed, have been observed in various 

 parts of the world. On the other hand, so far as x4.1bert county, New 

 Brunswick, is concerned, no rocks of volcanic origin are found in the 

 vicinity of the plaster beds ; pyrites and other sulphides are not notice- 

 ably abundant in the rocks of the district ; no sulphur springs are found ; 

 and the existence of acid springs at the time of the formation of the 

 gypsum is an assumption wholly without direct evidence in its support. 

 The view, though applicable in some instances and upon a small scale, 

 has been generally abandoned in relation to the larger deposits of gyp- 

 sum rock as being less in accordance with observation and experiment 

 than other views more receniiy advanced. 



(2) A second supposition is that the plaster deposits owe their 

 origin to the mutual reaction of natural sulphates, such as those of iron, 

 copper and magnesia, with carbonate of lime; but there is nothing 

 in connection with the Hillsborough deposits to give it support, and 



