



148 Mathews — Structure of the Piedmont Plateau. 



1859. According to this view the structure is a more or less 

 deformed synclinorium. This hypothesiSj together with the 

 second, is regarded as untenable by Williams on the grounds 

 enumerated in his paper on the subject, where he proposed the 

 third hypothesis as the most reasonable explanation of the facts 

 and the one to be accepted as most probable unless subsequent 

 explorations should render its modification necessary. 



At the time Williams proposed this hypothesis no part of 

 the Maryland Piedmont had been mapped by the IJ. S. Geo- 

 logical Survey, and the maps at his disposal consisted of inac- 

 curate road maps of the various counties. At this time also 

 the detailed mapping of the Piedmont, which was later prose- 

 cuted by him with success, had not been pursued beyond the 

 immediate vicinity of Baltimore, where the structure is some- 

 what exceptional. The conclusions drawn were based upon 

 several driving trips across the Piedmont Plateau in different 

 directions, and the generalizations reached, while brilliant for 

 the amount of information in his possession, are such as to 

 demand modifications as the detailed mapping of the Piedmont 

 on the scale of a mile to the inch by the Maryland Geological 

 Survey progresses. 



Results of Later Work. — Shortly after the publication by 

 Williams of the paper referred to, the writer commenced a 

 mapping of local areas under the former's direction and has con- 

 tinued field investigations as opportunity presented during the 

 twelve years, until fully 1200 square miles of the Piedmont 

 have been mapped on the scale of 1 : 62,500 and the entire Pied- 

 mont has been visited in economic work demanding greater or 

 less local detail. The work of deciphering the structure of 

 the Piedmont of Maryland is.b} 7 no means ended, but it is pro- 

 posed to give in the following pages what are believed to be 

 the general lines of structural uplift and depression across the 

 area. Many local questions still remain unsolved and much 

 detailed mapping is still necessary in the western portion of 

 the Plateau, but the views here expressed have been found to 

 present the most reasonable interpretation of the area studied. 

 Moreover, while they have been developed independently they 

 are found on comparison to be more or less in accord with the 

 structural interpretations resulting from the most recent work 

 in corresponding areas to the north and south. 



The methods employed in the investigation of the Piedmont 

 geology embrace a consideration of all of the data available 

 under the conditions encountered. The region considered lies 

 south of the zone covered by the continental ice, and as a con- 

 sequence few exposures of fresh rock are encountered except 

 in the recent stream cuttings or in artificial openings. At the 

 same time, bowlders and disintegration products found on the 



