The analysis of the seismograms of an explosion of 4,000 tons (about 10 million pounds) of munitions piled up in tunnels 50 feet below the surface of the rocky island of Heligoland in the North Sea near Hamburg, Germany, and of a great number of natural earthquakes, especially the disastrous shock at Messina (Italy) led to the discovery of a number of formations unknown heretofore down to a depth of several hundred kilometers. At depths from 110 to 118 km a plastic layer occurs which seems to represent a belt around the globe. At a depth of 183 km the melting point of a material with very high wave-velocity is reached. These findings are in accordance with the determination of the depth of Isostatic Surface by Hayford and Helmert (both in 1909) from deflections of the vertical and/or from gravity anomalies (113 and 118 km, respectively). Qualitatively, the results are also in accordance with the assumption of Gutenberg and Richter, based on the measurement of the amplitudes of the first recorded waves from numerous earthquakes with different epicenter distances and with different depths, that at a depth of 80 to 100 km the melting point of the material has been reached.