As previously stated, Wanless was a sedimentologist. He somehow found time to be a highly productive researcher despite being busy with teaching. He studied many topics including Paleozoic rocks of Illinois, especially the late Paleozoic; Carboniferous – Pennsylvanian rocks which contain large coal deposits. He later expanded his work on these rocks from Illinois to adjacent states and then all of North America and branched out even further to study these coal-bearing rocks in Europe and Australia. His interest was primarily their origin, petrographic character, and the repetitive cycles they exhibited.  His theories of cyclic sedimentation and of the environment in which the rocks were deposited gained world-wide acceptance and acclaim. Among his more than 150 reports, several were major USGA publications, including; Bulletin 57, “Geology and Mineral Resources of the Alexis Quadrangle” published in 1929, and Bulletin 82, “Geology and Mineral Resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles”, published in 1957. Other important reports include “Pennsylvanian Faunas of the Beardstown, Glasford, Havana and Vermont Quadrangles” and “Classification of the Pennsylvanian Strata of Illinois with R.M. Kosanke, J.A. Simon, and H.B. Willman” His primary research topics were Pennsylvanian geology of Illinois, Appalachian basin, southwestern United States; cyclic sedimentation; environmental mapping of Paleozoic strata; Late Paleozoic glaciation; South Dakota Oligocene; stratigraphy of northwest Wyoming; and geologic photo-interpretation, especially of coastal changes. Out of all of his books, some can still be purchased today from the GSA despite them being published decades ago. The fact that his work is still relevant today is a testament to how remarkable of a researcher Wanless was.