418 SKY. MINERALS. 



is true that large tracts of rock are every where found 

 without presenting this appearance of contained water ; 

 yet it may still remain a doubt whether their ordinary 

 dry condition is not limited to a certain distance from 

 the surface ; as even in the operations of quarrying or 

 mining we can only attain to a moderate depth within 

 that time in which the portions successively exposed 

 would acquire the hard state. Nor indeed have mine- 

 ralogists paid mudi attention to a circumstance, which 

 however well known to occur in many familiar instances, 

 has hitherto been overlooked and treated as an accident.* 

 I may add a few wofds/elatirig to the marble of Strath, 

 of which the following varieties are the most remarkable. 



1. Pure white marble, the fracture intermediate between 

 the granular and small platy. 



2. The same with a scarcely discernible shade of grey. 



3. The same with variously disposed veins of grey and 

 black, resembling the common veined marble used in 

 architectural ornaments. 



4. The same with narrower veins, well defined, and 

 often reticulated with a great semblance of regularity. 



5. The same, distinguished, independently of the veins, 

 by a parallel and regular alternation of layers of pure 

 white and greyish white. 



* The fact now noticed presents useful hints with regard to the quar- 

 rying of rocks ; although well known to workmen, it has not been turned 

 to the uses to which it might have been applied. Antiquaries have been 

 at a loss to account for the works of the ancients in granite, when the use 

 of steel, if not absolutely unknown, was assuredly not general ; neither 

 its properties nor the method of making it having been ascertained, 

 so as to render it a common material. As their columns appear to 

 have been wrought in the quarries, it is probable that they took advantage 

 of the natural softness which even granite in this state possesses. To 

 apply the principle to use at present, it would be proper to keep tlie 

 quarry in a moist state, or, if the blocks must be removed from it before 

 working, to immerse them every night in water; or else, by some other 

 expedient of watering, to prevent them from losing by evaporation 

 their natural moisture until they were finished. 



