34 Introduction 



In a general way the present outline of the ]!^orth American Continent 

 has been maintained since the beginning of the Paleozoic era. It is 

 probable, however, that throughout the Paleozoic the eastern margin was 

 of wider extent, since almost no rocks of this era are known along the 

 Atlantic slope of the old land mass Appalachia. To the north of this 

 ancient land was another known as Acadia (includes Taconia and Nova 

 Scotia, see Plate lY). This has been subjected to much lateral pressure 

 and during the Paleozoic it was undoubtedly mountainous, the Atlantic 

 often invading the region between the ranges. Many times during that 

 era these lands were thrust upward and landward by the settling or deep- 

 ening of the Atlantic Ocean, due to the periodic shrinkage of the earth, 

 Acadia being more frequently thus acted on than Appalachia. The thrust- 

 ings again and again renewed the elevation of the lands, enabling the re- 

 juvenated streams that flowed from the latter to deposit their loads of 

 muds, sands, and lime, which are now seen as the shales and slates, sand- 

 stones and quartzites, limestones and marbles, throughout the State of 

 Maryland. During most of the Paleozoic, eastern Maryland figured as 

 part of Appalachia and what was here worn away by weatlier and rain was 

 dumped by the then existing streams into the Appalachian Sea. The 

 eastern shore of this interior sea was originally some miles east of 

 Harper's Ferry, and by the time the Devonian was reached it had 

 made its way west to North Mountain. From late Ordovician time 

 to near the close of the Mesozoic era, Maryland was land east of Harper's 

 Ferry, to far east of the present shore. The lands within the Paleozoic 

 continental seas of North America and those bounding them are shown on 

 Plate IV. It should be understood, however, that this map is a synthetic 

 one and does not illustrate any definite period. The areas designated are 

 those least subject to the invasion of Paleozoic continental seas. 



The marine waters that have invaded Maryland are extensions of the 

 oceans, in the east as more recent overlaps of the Atlantic and in the west 

 as the Appalachian Sea of Paleozoic age. The latter body of water at 

 times connected with the Atlantic but more often with the Gulf of Mexico 

 and other waters that came from the Pacific and Arctic oceans. These 

 overlaps and seas were all shallow, and constitute the continental seas of 

 Dana, so named because they lie on the continent and not in i 



