140 On the Paragenetic Relations of Minerals. 



frequent association, under similar conditions, of fluor spar 

 and heavy spar. Undoubtedly it is not allowable to form an 

 opinion on this subject from individual specimens in mineralo- 

 gical cabinets ; it is the universal association of minerals in 

 the different known lodes of one class which must be studied. 



Moreover, the determination of lode formations is not alone 

 difficult in regard to the constituent minerals, but likewise 

 in regard to the date of the several substances. When dif- 

 ferent formations occur together in one lode, or in different 

 lodes intersecting each other, some inference may be formed 

 as to their relative dates ; but as yet there are only a few such 

 instances of contact known, and therefore this branch of re- 

 search, so important in its relation to mining, yet remains to 

 be cultivated. 



The following description of lode formations comprises 

 both such as have a practical interest, and such as at present 

 have only a scientific interest ; they are likewise arranged 

 according to probable relations of date, commencing with the 

 older. 



I. Pyroxene, garnet, pyrites, and blende formation. — This 

 is undoubtedly one of the oldest, perhaps the oldest, of all 

 lode formations, although want of acquaintance with its con- 

 tact phenomena renders this still uncertain. The character of 

 these lodes is not very distinctive, since the lode planes are 

 frequently parallel with the strata adjoining ; for which rea- 

 son they are very generally regarded as beds. Again, the 

 banded structure is almost altogether wanting. The forma- 

 tion, however, is marked by the occurrence of silicates, some- 

 times in considerable masses ; a circumstance which strongly 

 indicates a very remote date. It is probable that the lode 

 substance of this formation bears a relation to the adjoining 

 rock similar to that of amygdaloid rock to old red sandstone, 

 where it has penetrated the latter, and yet occurs in parallel 

 layers. Thus the date of the lode substance would be much 

 the same as that of the adjoining rock; and indeed, in a 

 geognostic point of view, it appears to resemble the eruptive 

 rocks, as if it had been injected, which may be the reason of 

 the absence of banded structure. 



This formation occurs in Saxony, Bohemia, and Scandi- 



