On the Paragenetic Relations of Minerals. 347 



any more. This phenomenon is remarkably distinct in the 

 " bandzwittern," at iUtenberg (Saxony). The pseudomor- 

 phous tin ore, after feldspar, from Cornwall, appears to be of 

 interest in connection with this fact. 



Granite ought to be more generally examined for tin ore ; 

 for not only is it probable that many granites contain enough 

 of the finely-disseminated ore to be worked advantageously, 

 but likewise this circumstance may serve as a clue to the dis- 

 covery of lodes. Moreover, the presence of beryl, topaz, 

 wolframite, &c, should not be overlooked, as these minerals 

 are frequent associates of tin ore. 



Professor Breithaupt is inclined to doubt the existence of 

 beds of tin ore. The deposits of this ore in the granite of 

 Zinnwald, which have been regarded as beds, certainly present 

 some such appearance. But those which make but a very 

 small angle with the horizon are intersected by a true lode, 

 possessing in every respect similar characters. The loose 

 fragments and the masses of fractured quartz crystals, ce- 

 mented together by subsequently-formed quartz found in 

 these deposits, render it probable that they are true lodes, 

 which, together with the rocks, have suffered such an altera- 

 tion of position as to become more or less horizontal. 



It has already been stated, that many minerals occur, both 

 imbedded in rocks and upon lodes, and they perhaps furnish 

 the strongest evidence of lateral secretion. 



The extraction of certain constituents of the lode minerals 

 from the adjoining rocks would appear to have been more 

 easy in schistose and stratified rocks, on account of their 

 structure, than in the massive rocks, — granite, syenite, por- 

 phyry, &c. It is perhaps for this reason that lodes are more 

 frequent and richer in such rocks. Tin lodes are more fre- 

 quent in the schistose than in the massive rocks. Both gra- 

 nite and the older gneiss have probably originated from the 

 same primitive mass, but no disseminated tin ore has ever 

 been found in either mica or clay slates, although it may 

 have been present in those instances where it occurs in lodes 

 in these rocks. Lodes which do not bear tin ore are still 

 more rare in massive rocks. However, it must not be in- 

 ferred from this that all tin ore has been formed by lateral 



