The Cannonball Marine Member of the Lance Formation of North and South Dakota and Its Bearing on the Lance-Laramie Problem

Abstract

Field examination by the writers and the paleontological determinations by Drs. Stanton and Knowlton during the years 1912 and 1913 show that in a large region west of Missouri River in North and South Dakota the Lance formation consists of two distinct parts, a lower non-marine part containing a flora very similar to, if not identical with, that of the Fort Union and an upper marine member containing a fauna closely resembling, but not identical with, that of the Fox Hills sandstone. This upper part, on account of its peculiar fauna, has been mapped separately and named the Cannonball marine member of the Lance formation. Farther west non-marine beds bearing lignite and occupying a similar stratigraphic position have been named the Ludlow lignitic member of the Lance. The area examined by the writers embraces a territory of over 5,000 square miles, extending from Mandan, North Dakota, west to Montana, a distance of about 175 miles (Fig. i), and south beyond the boundary line of South Dakota. The marine member of the Lance has been mapped from Mandan to a point 4 miles west of Haley, North Dakota, a total distance of about 130 miles. A large part of the area examined by the writers has been described already from an economic standpoint.2 The Lance formation had previously been mapped in two adjoining regions, the Bismark Quadrangle3 and the Standing Rock