A Very important discovery was made independently by Mr. Davison, and somewhat earlier by Mr. T. Mellard Reade, when they demonstrated that, on the hypothesis of the earth having cooled as a solid body, there is within it a certain level, which is called by Mr. Davison the “ surface of zero-strain,” and for which Mr. Reade has adopted the term “ level of no strain.” At this level compression ceases, and for a certain distance beneath it extension, or stretching of the layers of the globe, takes the place of compression.