Ten weeks during the summer of 1939 were spent in collecting from the fossiliferous horizons of the Pitkin, mapping the formation at its most northern and southern exposures, and in studying the stratigraphic and structural features. This work was conducted along the escarpment of the Boston Mountains from Batesville to Fayetteville in Arkansas, and since the Pitkin is known to crop out in Oklahoma, some time was spent examining the formation from the Arkansas state line to Muskogee, Oklahoma. The winter of 1939-1940 was spent at the Univeristy of Chicago in studying the fauna and in interpreting the results of the field work. After formal acceptance of the thesis by the University of Chicago, additional work was done augmenting some parts and modifying other parts of the text.