The following notes have been recorded with the idea of showing that a field relationship exists between true chert veins or aggregations, and certain igneous intrusions. Beyond the fact that the cherts have been formed probably as the result of some hydrothermal agency, usually associated with, and occasionally the result of, volcanic episodes, it is not possible to enter more fully into the geological origin of this form of silica. Microscopic fossils have been observed and recorded from the cherts of Santa Elena, but the presence of these organisms may be accounted for by the fact that certain Radiolaria are able to exist in waters of a fairly high temperature, it is also possible that these fossils may have been abstracted from the vein walls of the country rock during the secondary process of infilling by crypto-crystalline silica.