406 
MR. R. W. FOX ON THE ELECTRO-MAGNETIC PROPERTIES 
t lie horizontal transfer of the electricity may be much impeded, it does not 
seem to be wholly intercepted. The quartz contained in cross veins is usually 
of a fibrous or radiated texture, and differs materially from that found in the 
east and west veins. 
All our mining districts abound more or less with veins or dykes of a rock 
generally possessing a porphyritic character, termed by the miners “ Elvan 
courses.” Their width is extremely various, sometimes as much as fifty fathoms 
and upwards. Their direction in general is nearly N.E. or E.N.E. to S.W. or 
W.S.W., and their underlie is with few exceptions towards the N.W., and at 
various angles from the perpendicular, often exceeding 45°. They are pene- 
trated by ore- veins in almost every direction, from their greater underlie, and 
usually more considerable deviation from an east and west bearing than the 
latter. It has been observed that copper and tin lodes generally become 
changed in quality whilst in the elvan*; and indeed this remark applies to 
any change of rock : thus a vein productive in granite commonly becomes 
barren in killas, and vice versa. 
Many of the phsenomena above referred to, bear striking analogies to com- 
mon galvanic combinations, and the discovery of electricity in veins seems to 
complete the resemblance. 
I have been informed by intelligent persons who have visited some of the 
mining districts of Mexico, Guatimala, and Chili, that there is a general resem- 
blance between the veins, elvan courses, & c. in some parts of those countries 
and our own ; and I think it has been noticed by Baron Humboldt, that the 
st ratification of primitive rocks in different, and far distant parts of the world, 
has a general tendency from the N.E. towards the S.W. 
Such analogies become highly interesting when regarded in connection with 
terrestrial electricity, magnetism, and heat; for if it be granted that the two 
latter increase in intensity at great depths in the earth, they are evidently 
so connected with electrical action that the augmentation of it also, in the 
interior of the globe, may be reasonably inferred. 
However this may be, assuming that metalliferous veins exist more or less in 
primitive rocks generally, (and experience favours this assumption, whether we 
It lias been remarked of copper lodes, that they are often improved in quality whilst in elvan, 
particularly if it be not very hard. 
