Numerous investigators in recent years have called attention to regularly recurrent sequences in the strata of the Pennsylvanian system in the eastern and central parts of the United States. Wanless, in association with J. M. Weller, has been engaged for several years in field studies of the Pennsylvanian in Illinois and surrounding states, for the Illinois State Geological Survey, and has traced many of the recurrent sequences or cyclothems1 over wide areas, using them as an aid in correlation. Reconnaissance studies have also been made by him in Ohio, Kentucky, Indiana, and the northern mid-continent and Rocky Mountain regions. Shepard has suggested the basic idea as to the cause of the cycles developed in this paper and has contributed information from studies of recent sea level oscillations and the influence of these changes on continental shelf sediments.
The authors have attempted to determine whether this peculiar type of sedimentation . . .