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measuredin an aqueous alkaline solution with an excess of ligands. The experimental data least-squares method on the assumption that the energy separation between _J-levels of the 4fn-It has been known that the radial integrals of the valence orbitals of a metal ion decrease when the free metal ion combines with ligands to form a metal complex.1) This phenomenon is called the nephelauxetic effect, which means the expansion of electron clouds; it may be regarded as a measure of the covalency of coordination bands.1) Although the nephelauxetic effect has been extensively investigated in d-transition metal complexes, the study of f-transition metal complexes has been rather limited because of the theoretical and experimental difficulties.which are attributed to the electronic transitions within the 4fn-configuration (n=2-12), are shifted when the environment of the ion is changed. This is undoubtedly an indication of a change in the ions the spin-orbit interaction can not be neglected and the radial integrals should be treated by an intermediate coupling scheme.3) The separation between J-levels of the 4fn-configuration may be expressed in terms of the radial integrals (f)4) and the spin-orbit coupling parameter.

Five types of ESR signals were observed in shales. The resonance composed of six lines near geff = 2 (type A) is attributed to Mn(II). Type A resonance is divided into two groups on the basis of its line shape; one exhibits six sharp lines (type A-1), and another shows relatively broad lines (type A-2). The geff = 2 broad resonance (type B) may be attributed to Fe(III). The geff = 2 sharp resonance line (type C) probably results from stable organic free radicals. The geff = 4.1 resonance (type D) can be attributed to high spin Fe (III) occupying sites of orthorhombic symmetry in clay minerals. Some of the shales show an inclined signal covering a wide magnetic field (type E).Combination of ESR measurements and leaching experiments made it possible to survey the distribu tion and states of some elements in shales. In shales which exhibit type A-1 resonance overlapped with type A-2 resonance, Mn (II) is randomly distributed both in calcite and clay minerals. In shales which exhibit only type A-2 resonance, Mn (II) is associated mainly with clay minerals. Most of the iron in shales is bound to clay minerals. A part of the iron in clay minerals is present as Fe (III) which shows type D resonance.