The results of numerous resistivity soundings from all parts of Iceland are analyzed. The resistivity and the P wave velocity of the uppermost kilometer in the crust show a strong correlation with the geological structure of Iceland. By estimating porosity from P wave velocity, Archie's law is found not to be valid in general. The temperature dependence of nine water-saturated basaltic rock samples was investigated in a laboratory showing stronger temperature dependence than expected from pore fluid conduction. These two facts suggest that interface conduction is the most important conduction mechanism. A relation between bulk resistivity, fracture porosity, pore fluid resistivity, and temperature is established. Comparison of regional bulk resistivity with different zeolite zones shows that the resistivity is mainly a function of the maximum depth of burial of the lava pile, emphasizing the importance of clay minerals and zeolites for the measured bulk resistivity.