The Paragenetic Relations of Minerals. 85 



the sky was also cloudless, but in the evening the air was 

 misty. 



Dr Davy considers that the carbonaceous deposit or soot- 

 like film occasionally observed on the lakes of Westmore- 

 land, is really of the nature of soot, derived from the adjoin- 

 ing manufacturing districts, wafted thither by the wind, and 

 falling with the mist or light rain. The film burns in the 

 same manner as soot, sinks when wet in water, imparts a 

 brownish hue to transmitted light, and, under the microscope, 

 appears to be composed of particles more or less irregular in 

 form, varying in size from ^oV o^h to T15 \ q th of an inch. Dr 

 D. further thinks that the precipitation is an ordinary rather 

 than an uncommon occurrence here, as is shewn by the dis- 

 coloration of the sheep of the country, especially after ex- 

 posure of many months on the higher fells. Seen on the 

 mountain pastures, or, when driven into the lower meadows 

 in the early spring, their coats are of so dark a hue, as to 

 resemble closely those of their fellows fed in the most smoky 

 precincts of our great towns ; and, on examination, the 

 colouring matter staining the fleece is found to be similar to 

 that of the black film of the lakes and tarns, and, in brief, it 

 is essentially soot.* 



J. F. Miller. 



Observatory, Whitehaven, 

 April 1853. 



On the Paragenetic Relations of Minerals. 



(Continued from page 323 of vol. liv.) 



Although with regard to the majority of minerals and rocks 

 which present a porphyritic structure, the inference to be 

 drawn from the before-mentioned facts is, that the formation 

 of the imbedded substances has been subsequent to that of the 

 entire mass, and probably even to the perfect solidification of 

 the matrices, it is undoubtedly necessary to take a different 



* Edinburgh Philosophical Journal for January 1852, p. 64, and private 

 letter from Dr Davy. 



