Earth conductivity is far more dependent upon the presence or absence of moisture than upon the particular nature of the material which composes it other than water.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
Like two faces looking at one another through a sheet of glass they were close together, almost touching, but they could not hear or feel each other: the conductivity between them was broken.
"The Greater Inclination"
Edith Wharton
Copper tacks should be avoided on account of their superior conductivity.
"The Electric Bath"
George M. Schweig