Diallage Rock of Shetland. 1 09 



The aspects of these mixtures vary much, according to the 

 magnitude of the parts and the relative proportions of the con- 

 stituent minerals. 



B. Diallage and actinolite. 



C. Diallage and talc, or chlorite. 



In this mixture, it is seldom easy to determine whether the 

 mineral mixed with the diallage, is talc or chlorite ; but both 

 of them seem to occur. 



D. Diallage and Serpentine. 

 When this compound occurs as a transition between serpen- 

 tine and strata of diallage rock, it contains so much diallage as 

 nearly to exclude the serpentine. It may, however, be con- 

 sidered also as a variety of serpentine. 



Third Division^. Composed of three Ingredients. 



A. Diallage, feldspar, and mica. 



B. Diallage, feldspar, and quartz. 



These compounds are rare in Shetland, and are indeed rather 

 incidental than found in extensive masses. 



If there is a quaternary compound of diallage, feldspar, 

 quartz, and mica, it has occurred to me so rarely, and in a 

 manner so limited, that I am yet unwilling to consider it as 

 deserving a place among the varieties of this rock. 



Diallage rock occasionally contains imbedded portions, or 

 limited veins, of talc, chlorite, actinolite, asbestos, and steatite ; 

 but I am not yet aware that it contains, either these, or any 

 other minerals, embedded or intermixed in such a manner as to 

 modify its general character. 



Art. XI. Observations on Aroma. Being the substance of a 

 Paper read by M. Robiquet, to the Philomathic Society 

 of Paris, 



BoERHAAVE attributed odorous emanations to a subtile 

 fluid, which he regarded as capable of exerting great influence 

 on the phaenomena of vegetation and the animal economy, and 



