Geological remains are conserved mainly either together with living beings for the sake of the integrity of nature or for their economical or aesthetic value. However, they also have scientific value for the geologist to reconstruct the earth's past. For this reason we propose a model which is an application of marginal utility theory in economics and takes into account the informational utility of geological remains. Informational utility of geological remains ranges over their geological significance which is induced by the importance of the geological processes that produce them, and over their spatial extensiveness. Our model takes into account also the cost and budget of conservation and proposes to solve the differential equations of informational utility and cost simultaneously in order to obtain the optimum quantity of the remains to be conserved.