STRUCTURE AND STRUCTURAL RELATIONS 343 



action would be likely to produce folds of shorter major and greater 

 minor axes than are the rule in the long-drawn-out ellipsoids of Appa- 

 lachian folding. The effect of these forces must thus have a direct ex- 

 pression in the areal distribution of the various deposits found in the 

 Piedmont of Maryland, and, conversely, if such results are found there 

 is developed a reasonable probability that the present major structures 

 of the Maryland Piedmont were produced by the same forces and at the 

 same time as the Appalachian folds. 



Starting on the west with the faulted and sharply folded anticlines of 

 the Blue Ridge bordered on either side by Cambrian rocks and associated 

 igneous masses (compare figures 1 and 2), one may pass successively 

 eastward through Maryland across the gently eastward sloping lime- 

 stones of the Frederick valley, which in turn, as above described, appear 

 to dip under the so-called semi-crystallines or phyllites of the Piedmont. 

 While the detailed structure is not fully known, it seems probable that 

 there exists in this part of the state a very open general structure by 

 which the beds lie almost horizontal in their major folds, with a much 

 compressed subordinate structure, which, because of the numerous minor 

 folds, give to the rocks an appearance oi highly inclined and complicated 

 folding. East of Parrs ridge the rocks are more crystalline and the fold- 

 ing a little more pronounced in its general features, with a change in 

 strike of the axes of the major folds in conformity with the change of 

 direction in the continental folding previously described. Between the 

 area of open folding just described on the northwest and the cover of 

 Coastal Plain deposits on the southeast one may readily recognize in the 

 Maryland area the broad synclinal trough of the eastern phyllite belt 

 and that of the Cocke3 7 sville marble, separated by the dome-like anti- 

 cline of the Baltimore gneiss already described. Still farther east, sepa- 

 rated from the Cockeysville synclinorium in part by a southern anticlinal 

 border of Baltimore gneiss, is a broad zone of igneous rocks composed 

 of gabbros, granites, and other plutonic types which occupy most of the 

 eastern border of the Piedmont between Wilmington, Delaware, and 

 Laurel, Maryland. 



Minor igneous masses are found with the same general trend, and these 

 are seen to be rather closely associated with the structure lines of the 

 region, occupying as they generally do anticlinal axes. This relation 

 to the structure lines is particularly shown in case of the long belt of 

 serpentines extending from Lancaster county, Pennsylvania, across the 

 Susquehanna river almost to the nose of the northern anticline of the 

 Baltimore gneiss. Farther to the southwest, almost on the strike of this 

 anticlinal axis, begins a long and somewhat narrow body of granite ex- 

 tending from Sykesville, on the Baltimore and Ohio railroad, southward 



