1. A third definition of the crust has been given by BENIOFF, see end of Sect. 4.
2. For the typical Heligoland explosion of 18 April 1947, when 4000 tons of high explosive were fired, see P. L. WILLMORE [Phil. Trans. Roy. Soc. Lond., Ser. A 242, 123 (1949)]. G. A. Schulze and O. Foertsch [Geolog. Jb. 64, 204 (1950)]. H. Reich, O. Foertsch and G. A. Schulze [J. Geophys. Res. 56, 147 (1951)]. The exact depth of the Mohorovicic discontinuity was disclosed with unprecedented clarity
3. J. H. Hodgson: A seismic survey in the Canadian shield. Publ. Dominion Obs. Ottawa 16, 113–163 (1953).
4. P. L. Willmore, A. L. Hales and P. G. Gane: A seismic investigation of crustal structure in the Western Transvaal. Bull. Seism. Soc. Amer. 42, 53–80 (1952).
5. H. E. Tatel, L. H. Adams and M. A. Tuve: Studies of the Earth’s Crust Using Waves from Explosions. Proc. Amer. Phil. Soc. 97, 659–699 (1953).