During the past two seasons I have been engaged in making a detailed study of the sedimentary formations of a portion of the Black hills of South Dakota and Wyoming. The principal observations were made in the southern half of the area, but some atttention was given to the northern extension of the Mesozoic formations. The fossil fish described by Doctor Eastman in his paper, which immediately follows this one, were discovered in 1898 in the Jurassic beds near Hot Springs, South Dakota, near the southern margin of the region.
The Black Hills uplift is an irregular dome-shaped anticlinal, having in its more obvious features an oval area 120 miles in length and 60 miles in breadth, with its larger dimension lying nearly northwest and southeast. It is situated in the great east-sloping plain that extends from the Rocky mountains to the . . .