MaUYLAXD CiEOLOCilCAL SlliVKV 33 



frequently appear as great waves fixed ujioii a sea wiiieli stretelies as far 

 as the eye can reach. The less rugged scenery of tlie Appahicliian IMateau 

 is at times scarcely less attractive. 



Tiie thickness of the Devonian of Maryland is about 11,<»()0 feet, com- 

 pared with '.MOO feet for the Silurian and :Vm) i'eet for the Carboniferous. 



PALEOGEOGRAPHY OF THE DEVONIAN ' 



I'aleogeography treats of ancient or geologic geography, the word hav- 

 ing been first used by the Phiglish paleontologist Eobert Etheridge, in his 

 presidential address before the Geological Society of London in 1881. 

 Paleogeographic maps, however, were made long before the word origi- 

 nated, the first one having been constructed in 18(13 by the late Professor 

 James D. Dana. Since that time u|)ward of 3.")0 such maps have been 

 published, about half of which relate more or less directly to North 

 America. 



If restricted to base maps of the State, the paleogeography of Mary- 

 land would teach very little. To understand the various ancient in- 

 vasions of the seas and oceans into this region, it is necessary to know 

 the connections with marine waters that have at different times flooded 

 the North American Continent. These constitute extensions of the Gulf 

 of Mexico and the Atlantic, Arctic, and Pacific oceans. In the study of 

 any fossil fauna, either from the biologic or evolutionary or from the time 

 or stratigraphic side, its marine source or genetic relationship must be 

 known; until this is ascertained tiierc can be no certainty regarding 

 stratigraphic correlations with " standard sections." To this end, in- 

 formation has been accumulating for a century, and it is now possible to 

 make preliminary [jaleogeograpliic maps. Like all pioneer work, how- 

 ever, those here offered will doubtless undergo considerable change, yet 

 it is belie\ed that such changes will not be fundamental in character, 

 but rather those in which the plotted shore-lines will be altered, thus 

 causing the continental seas to take on other forms than the ones here 

 illustrated. 



' Contributed by Charles Schuchert. 



