Bulletin No. 23. The Limestones and Marls of Minnesota

Abstract

Minnesota has extensive deposits of calcium carbonate in the form of limestones, dolomites, and marls. This report deals primarily with the distribution and chemical composition of these carbonate deposits and the uses for which they are suited. The dolomites are the most widely distributed and the most readily available carbonate rocks in Minnesota. They are quarried in large quantities in the southeastern part of the state, where the lower Ordovician rocks are predominantly dolomitic limestones. Limestones high in calcium are far less abundant, being confined to several strata that are more limited in their distribution. Locally they have been quarried for their high lime content. The marls have been but very recently recognized as one of the valuable mineral resources of the state. These light, grayish muds underlie marshes, bogs, and lakes; they are not often visible at the surface. Most persons, therefore, are unfamiliar with the name, appearance, and distribution of marl. It can be distinguished from other muds by its light color, its abundant shell fragments, and its violent reaction with acid. The marl beds of Minnesota vary in thickness, but they are seldom more than thirty feet thick.