190 



.'! [LINES OF 1 II LEH 





igneous formations. lake lines of fault, with which 

 indeed they often coincide, inin . that is, veins 



filled with segregated minerals ,,f various kinds different 



FIG. 76. Map of part of the mining district of Gwcnnap, Cornwall, aa, granite ; 

 cc, the surrounding schistose rocks ; M, elvan dykes ; s, " greenstone "; w and 

 J,l, two sets of metalliferous veins, or lodes and cross-courses (De la Heche's 

 Geological Observer, p. 566). 



from the surrounding rock, do not in the majority of 

 cases attract attention at the surface. Their existence 

 must usually be determined from other evidence than 

 actual visible sections of them. If the geologist is at 

 work in a district where veins of this kind (jccur, he 



