After adverting to previous publications on the subject by himself and Professor W. B. Rogers, the author of the paper began the enunciation of the laws of structure of disturbed tracts of strata, by stating the general proposition that in all districts where thestrata have been displaced from the original positions or levels in which they were deposited, they invariably have the form of one or many waves, even where, from a flatness of the undulations, they seemed to retain their original horizontality.