§I. I ntroduction “ In South Devonshire the rocks are greatly disturbed, broken by faults, standing at various angles, folded, and distorted ; eruptive rocks frequently cut through them, and beds of volcanic ash are interstratified with them, Hence has arisen great dispute and uncertainty as to the true order of succession of deposits, although their fossils were referred to the Devonian age nearly fifty years ago. It will be seen without comment that the South Devonshire sections, from which most of the Middle- and Lower-Devonian fossils have been obtained, are valueless for determining the order of sequence of the faunas. There are many places (I saw such near Newton-Abbot) where limestones, appearing very similar in colour and structure, and within a stone's throw of each other, hold distinct faunas. In fact, the interpretation of the order of the beds is a matter of the greatest difficulty, even when occasional fossils appear.” Here is the geology of South Devon as epitomized by Professor H. S. Williams, of Ithaca, N.Y., in a paper read before the American Association for the Advancement of Science as lately as Aug. 30, 1889. Explorations in the rocks of Devonshire gave rise to the Devonian System; explorations in France, Belgium, Germany, Russia, and North America have made us acquainted with the succession of the Devonian faunas, and the extraordinary persistence of homotaxcous horizons, such as those characterized by Stringocephalus , Rhynchonella cuboides , and Goniatites , at the same time presenting us with the varied evidences of stratigraphical succession. The