MARYLAND GEOLOGICAL SURVEY 45 



The subject of ancient or geologic geography for which the term 

 " paleogeography " was proposed in 1872 by T. Sterry Hunt and was 

 prominently employed by Robert Etheridge, the English paleontologist, 

 in 1881, has become such an important branch of stratigraphic geology 

 that to-day no general stratigraphic discussion is complete without an 

 attempt to indicate the distribution of the land and water of the time. 

 Since 1896 when Canu published his " Essai de paleogeographie " the 

 term has been frequently employed. 



Paleogeographie maps have been prepared in America since 1863 when 

 James D. Dana published several generalized sketches of the Azoic, 

 Cretaceous, and early Tertiary periods, in the first edition of his Manual 

 of Geology. Since then over 500 paleogeographie maps have appeared, 

 about one-half of which refer to North America. Until recent years most 

 of these maps were subject to the criticism that they covered too much 

 time and therefore were too generalized. 



Schuchert, in 1908, in his " Paleogeography of North America," pub- 

 lished a series of maps based upon the most precise correlations and the 

 narrowest time limits that had hitherto been attempted. This work, 

 which was prepared in collaboration Avith all the leading American 

 stratigraphers and paleontologists, brought out with excellent clearness 

 many new features, especially the oscillatory nature of the continental 

 seas. This publication marks a great 'advance in the science of paleo- 

 geography. In spite of efforts to the contrary, some of these maps, as was 

 recognized by their author, covered too long a time period, and are subject 

 to the criticism just mentioned. 



Since 1908 a great amount of new data on the stratigraphy and 

 paleontology of American early Paleozoic formations has been accu- 

 mulated and to-day maps covering the geography of a single formation are 

 possible. Maps illustrating the early Paleozoic divisions of the geological 

 column were prepared by E. 0. Ulrich and revised at frequent intervals 

 as new facts were obtained. But few of these have hitherto been pub- 

 lished, but the writer has obtained permission to reproduce in this volume 



