HOW ON LIMESTONE AND MARBLE. 65 



and also a mottled white ; at Parrsboro' a purple rock is met with 

 and no doubt it pi'esents other varieties elsewhere. Its greatly supe- 

 rior hardness at once distinguishes it from the ordinary plaster, It 

 is used in this neighborhood (Windsor), in building the foundations 

 of houses. At the International Exhibition two specimens of the 

 Windsor hard plaster were shown cut and polished : one gave a 

 finely clouded surface and the other was rather uniformly spotted; 

 both were grey, and one showed in some lights a slightly bluish 

 tint : the edges of both at the meeting of the polished surfaces were 

 remarkably sharp and perfect. Since sulphate of lime (the chemi- 

 cal name of plaster) is not insoluble in water, polished surfaces of 

 hard plaster would lose their lustre in the open air, and the mate- 

 rial can only be used when cut and polished in in-door work ; under 

 these circumstances it may prove more durable than marble, which 

 is said to be so subject to change from variations of temperature that 

 the mantle of a chimney piece immediately over the fire is invariably 

 in a crumbling condition long before the sides or those parts which 

 are not so exposed to heat. This statement is given in Hunt's Hand- 

 Book to the International Exhibition (Vol. I, p. 325), and we find 

 there also (p. 332) in a very interesting passage, that some alabaster, 

 a variety of soft plaster, is more durable than Purbeck marble. The 

 author says " notwithstanding alabaster is decidedly so soft a sub- 

 stance that it may be easily cut with a pocket-knife, or abraded 

 with the nail, it is nevertheless an extremely durable material, if 

 not openly exposed to the weather. In most of the large churches 

 in the south of England, especially in Westminster Abbey, there are 

 instances of monuments constructed with Purbeck marblfe, and orna- 

 mented with alabaster tracery, niches, canopies, and little figures, 

 which are almost without exception perfectly free from decay ; an- 

 gles sharp, surface smooth, colour scarcely altered ; while the 

 Purbeck, a harder material, upon which the alabaster is fixed, has 

 scarcely any of the original surface left : although these two sub- 

 stances are close together, equally exposed to the same atmospheric 

 influences of damp and dry, summer and winter, from the fifteenth 

 or sixteenth century, to the present time, yet one is apparently un- 

 altered, while the other is certainly perishing, disintegrating, and 

 gradually mouldering away." 



Having been led to the subject of alabaster, I may state that the 



