-SKY. MINERALS. 417 



necessary therefore to detail the results obtained from 

 these experiments, nor from trials with such minerals as 

 tremolite, asbestos, or sahlite, where the water might also 

 be supposed to exist in a detached state among the fibres 

 or laminae. To avoid any error from this cause, a speci- 

 men of compact white quartz was selected from a place 

 recently quarried, in which all the accompanying sub- 

 stances had been found to undergo a sensible loss of weight 

 after some days' removal. As it was free from rifts, thje 

 eventual loss could not be supposed to arise from detached 

 water. After careful drying it was exposed in a warm 

 dry atmosphere for four days, and at the end of that 

 time was found to have lost five grains, the previous 

 weight of the specimen having been 2250, a loss amount- 

 ing to ,022 per cent. I may add that this loss, although 

 so slight, was accompanied by a sensible diminution of 

 the translucent appearance of the surface ; which pre- 

 sented, when recent, a watery aspect, but acquired the 

 usual semi-opaque whiteness of common quartz after this 

 operation. I do not imagine that even this loss was .the 

 whole which it might have undergone had the experiment 

 been pursued, since the interior parts of so large a speci- 

 men and so compact a substance could scarcely have lost 

 their water in so short a time, 



We have not as yet had the means of discovering 

 whether the circumstance now mentioned is of a limited 

 nature, or whether it is universally prevalent in rocks. 

 Nor can we therefore determine of what importance it 

 may be either in their chemical or geological history. It 



laceous porphyry. When the rocks tire opened in their interior parts by 

 the operation of quarrying, these are often found so soft as to re- 

 ceive the impression of the fingers, but in a few days they acquire the 

 same hardness which they possess in their ordinary state. This occur- 

 rence is not uncommon in the extensive quarries of Rubislaw, where thr 

 depth of the sections and the rapidity of working enable the mineralogist 

 to obtain access to those; parts which havp not received the influence of 

 the air. 



VOL. I. F. IE 



