500 W. H. HOBBS — LINEAMENTS OF ATLANTIC BORDER REGION 



Susquehanna river. Owing to its short extent and the difficulty of rep- 

 resenting the facts on the map, this line does not appear in plate 45. 



Ohio line. — Another strongly marked lineament (oj) follows a direction 

 somewhat farther removed from the equatorial along the courses of the 

 Ohio river and the Roanoke river in Virginia. 



Characteristics of the Network of Lineaments 



From w T hat has been said it would appear that the dominant linea- 

 ments of the Atlantic coast region of North America are largely included 

 in a nearly meridional series and in two other series which make nearly 

 equal angles with this direction. Other lineaments which more closely 

 approach the equatorial direction vary more from one another and are 

 both numerically less important and less strikingly brought out. It 

 can hardly be regarded as accidental that in all of the three series the 

 spacing should approximate so closely to uniformity, or, w T hen intervals 

 of exceptional width occur, that they should constitute multiples of the 

 normal intervals. This uniformity of spacing is indicated in the numer- 

 ation adopted for the lineaments on the map. The normal interval of 

 the meridional series is in the latitude of Boston. about 40 miles; that 

 for the northwest-southeast trending series is about 75 miles, while that 

 for the northeast-southw r est series approximates 125 miles. As already 

 pointed out, some approach to uniformity of interval within a series 

 should be expected if the lineaments are to be referred to disjunctive 

 processes and if faults of similar magnitude are spaced with the same 

 regularity as are the joints with which they are genetically connected. 



Inspection of the map reveals the fact that the area to the east of 

 the Hudson-Champlain line is noticeably different, as respects the domi- 

 nance of its striking lineaments, from the area lying to the west of the 

 same dividing line ; since to the east of this boundary between physio- 

 graphic provinces, the control of topography and of drainage has been 

 exercised largely by the meridional direction. A rectangular or checker- 

 board structure is evident in the region of the middle Atlantic states, as 

 a result of the dominance of the northwest-southeast and northeast- 

 southwest elements. On a smaller scale this t}^pe of topographic devel- 

 opment is well exemplified in the Adirondack province (see plate 47). 



Evidence that Systems of regional Joints extend over wide Areas 



Comparatively few geologists have put on record the directions of pre- 

 vailing joints within the regions which they have studied. Until such 

 studies have been undertaken the fragmentary records now at hand must 



