GENERAL CHARACTERISTICS 361 



on the north side of Dulany valley in the vicinity of Blenheim differ 

 somewhat from those exposed farther west. The change is due in part 

 to the presence of a small area of intrusive meta-gabbro. 



The dips and strikes, as is customary in the Wissahickon formation, 

 are rather variable; but in their cumulative effect they show a syncline 

 overturned to the southward in the vicinity of Loch Raven and a gentle 

 normal syncline forming the ridge in the vicinity of the Jarrettsville 

 turnpike. Farther westward in the high land between Royston branch 

 and Green run the structure is more complex, and will be described in 

 more detail when discussing the structure in the vicinity of Warren. 



Structure 

 general characteristics 



The structure of the Cockeysville marble area is not thoroughly un- 

 derstood without a consideration of its relations to the general structure 

 of the eastern part of the continent.* As is well known, the general tec- 

 tonic lines extend northeast from the south across Virginia until they 

 reach the limits of Maryland, when the strike of the various formations 

 is deflected to a more easterly position, sometimes even becoming east 

 and west. This general easterly trend of the formations passes in a 

 broad band, reaching from central Pennsylvania to the Atlantic, and 

 gradually returns in New Jersey and New York to its original north- 

 easterly trend. The Maryland area, and particularly that portion north 

 of Baltimore, is in the concave side of this major fold, a fact which ex- 

 plains certain of the structures found within this area, which appear to 

 be somewhat unlike those described from other parts of the Piedmont 

 and which doubtless led the late Professor Williams to an accentuation 

 of the oval-shaped figures for his different formations. The occurrence 

 of the various forces involved in the curvature of the general structure 

 have produced locally within the Maryland area conditions favorable to 

 torsional deformation, since the lines of distribution of the forces are not 

 parallel, but slightly inclined to each other. It is for this reason, in 

 part, at least, that the various folds, which are usually very long and 

 narrow throughout the Appalachian region, are here rather short and 

 dome-like, with intervening areas of less compressed folding. The effects 

 of these differences in conditions will be brought out more fully in dis- 

 cussing the faulting. 



The structural character of the Cockeysville region has already been 

 given in describing the areal distribution of the various formations, but 

 it is well to recall the fact that it consists essentially of anticlinal domes 



♦These are more fully discussed by the senior author in the preceding paper, pp. 334-335. 



