The catalytic activity of four types of clay minerals, Amesite, Co-amesite, Synthetic Mica Montmorillonite (SMM) and Ni-SMM, was investigated by studying the isomerization reactions of C4 normal olefins and methyl and dimethyl alkyl cyclopropanes. Since Co-amesite catalyzed the rapid isomerization of 1-butene and cis-2-butene while amesite by itself was inactive, it was concluded that the activity was due to the presence of the cobàlt. Over Co-amesite, cis-trans rotation occurs much more easily than does double bond migration, which requires a higher temperature than the former. Very little activity for saturation was observed over this catalyst when hydrogen was present; however, the rates of the isomerization reactions increased substantially when hydrogen gas was mixed with the reactant. The low activity of cobalt for hydrogenation of n-butenes was reported earlier, and the increased rate of isomerization in the presence of hydrogen is very typical of activity characteristic of metallic catalysts. These two factors both supported the conclusion that cobalt is the only active center in the Co-amesite catalyst for these particular reactions. In the case of synthetic Mica-Montmorillonite and Ni-SMM, it was concluded that SMM catalyzes the isomerization of C5 cyclic compounds while Ni provides active sites for both the hydrogenation and H2-D2 exchange reactions. The product distribution observed over SMM for all these isomerization reactions were identical to those observed over an amorphous silica-alumina cracking catalyst. The mechanism suggested for silica-alumina, proton addition coupled with the elimination of any pathway that passes through an unstable primary carbonium ion, appears to explain the data for SMM. The catalytic activity of Ni for hydrogenation, as well as for its promotion of H2-D2 exchange reaction, is very typical of nickel catalysts. Mass spectral analysis was used to study the relatively small amount of deuterium incorporation into the hydrocarbon molecules.