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but how is it ascertained that the vein, whichbears clay only, is the same as the metal-liferous ?

In the neighbourhood of Alstone twoparallel veins are said to be shifted by across-course in opposite directions.

Near Redruth two copper lodes, those ofHuel Virgin and Huel Maid, meeting ob-liquely, are shifted by a cross-course, theone to the left, the other to the right.

Where a lode is really shifted by a cross-course, the latter will often contain por-tions of the former, and the direction ofthese indicates the direction in which thelode is shifted.

To identify two lodes in the same mineis often a work of considerable nicety, andyet I have met with practical men, whothink that the veins which bear calaminein Mendip are the same as those which,bear calcareous iron ore in the forest ofDean ; who identify the whin-dykes of theHebrides with those of Antrim; and recog-nize in the Isle of Man the same veinswhich have proved productive in Wicklowand in Swaledale.

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