Although few writers appear to have concerned themselves, in any careful way, with the question as to the conditions which determine the formation of the fissures in which dikes and veins are deposited, they commonly assume that these seats of the accumulations of igneous or aqueous deposited materials existed before the intrusive matter which has entered the rocks found its resting place. The aim of this paper is to present certain facts and considerations which serve to make the steps by which these structures were formed clearer than they now are. In this inquiry the phenomena of dikes will first be considered; after that, those of veins.
Even a cursory examination of dike phenomena will show the observer that so far as the fissures which these structures occupy are concerned they are divisible into three groups: Those which clearly follow the planes of preexisting . . .