An examination of the generally accepted theory of origin for stylolites has been made, first, on theoretical grounds and, second by applying it to observed features and relationships of stylolites occurring in the limestones of southern Indiana and the dolomitic limestones and dolomites at Lockport, N.Y. The solution theory not only fails to meet the theoretical requirements but likewise fails to account for many structures and relationships associated with stylolites. The contraction-pressure theory which has been advanced to explain the origin of type 2 (22-338) of cone-in-cone structures has been applied, with modifications, to the origin of stylolites. The occurrence of stylolites in sandstone and quartzite, as well as in the carbonate rocks, is readily accounted for by the contraction-pressure theory, which also explains the wide variation in form, structure, markings and other features of stylolites. A new marking found on stylolite columns at the Lockport locality supplies critical evidence supporting the contraction-pressure theory vs. the solution-pressure theory. The new marking is described as adhesion ridges.