346 E. B. MATHEWS — MARYLAND AND PENNSYLVANIA PIEDMONT 



explain the relative broadening of the Piedmont along the Virginia-Caro- 

 lina boundary, where the structures of the west are trending southwest- 

 ward and those on the east in a more southerly direction. 



Conclusions 



The preceding surve) 7, of the present state of knowledge regarding the 

 formations and structure of the Piedmont in Maryland would seem to 

 warrant the following conclusions : 



(1) The four formations recognized by Doctor Bascom in the Phila- 

 delphia area may be traced across the state of Maryland, and they prob- 

 ably constitute the bulk of the rocks forming the Piedmont of Virginia, 

 which have heretofore been mapped as a unit. 



(2) The structural character of the Piedmont from Trenton southward 

 to southern Virginia is similar throughout to the Appalachian structure 

 of the less metamorphosed Paleozoics to the westward — that is, one may 

 recognize within the Piedmont a series of long and narrow folds and 

 arches trending parallel to the trend of the Appalachians. An excep- 

 ion to this general rule is noticeable in the central Maryland area, which 

 lies toward the center of a local curve in the Appalachian structure, 

 where the structural forms are more nearly circular than is the general 

 rale in the Appalachians. 



(3) The age of the different formations in the Piedmont is still un- 

 settled, with the weight of opinion so far presented in favor of an early 

 Paleozoic age for the formations immediately overlying the Baltimore 

 gneiss. 



(4) The conclusions reached, so far as they relate to Maryland, are 

 based on a detailed mapping or intimate knowledge of practically all of 

 the Piedmont, but those of Virginia must be regarded as merely sug- 

 gestive and warranting credence only in so far as the principles of inter- 

 pretation established by detailed work for part of the province permit 

 of application to contiguous areas. 



