8io PRINCIPLES OF STRATIGRAPHY 



St. Lawrence, the Quebec, the Ottawa, and the New York. 

 The Frontenac axis separates the last two basins, and joins 

 the Adirondack dome to the Ontario dome. Northwest of the lat- 

 ter is the North Ontario dome, the Temiscaming syncline separat- 

 ing the two. To the north of this is the James Bay Basin. Next 

 southward of this series is the Alleghany basin, embraced by the 

 Alleghany land lobe of the Appalachians on the east. Northwest of 

 this is the Michigan basin, these two being separated by the Toledo 

 anticlinals. Northwest of the Michigan basin is the Wisconsin 

 dome, which is separated from the North Ontario dome by the deep 

 Superior synclinals. Southwest of the Wisconsin dome is the Iowa 

 basin, and southeast of this the Illinois basin, with the Keokuk anti- 

 cline between. The Illinois and Michigan basins are separated by 

 the Kokomo anticline. The Cincinnati dome is enclosed by the Illi- 

 nois, Michigan and Alleghany basins, and south of it is the smaller 

 Nashville dome, with small basins on either side. The southern 

 tier is formed by the Alabama-Mississippi basin in the embrace of 

 the Mississippi land lobe, the Ozark dome, and the Oklahoma basin. 



f. Dcfonnafions Due to Dislocation of Strata. Faulting. 



20. Faults. "A fault is a fracture in the rock of the earth's 

 crust accompanied by a displacement of one side with respect to 

 the other in a direction parallel with the fracture." (Reid, etc.-i8; 



"^A closed fault is one in which the two walls of a fault are in 

 contact." 



"An open fault is one in which the two walls of a fault are sep- 

 arated. The same fault may be closed in one part and open in 

 another." 



"A fault surface is the surface of fracture. It is rarely plane, 

 but where it is without notable curvature over any area it may be 

 called a fault plane for that area. 



''A fault line is the intersection of a fault surface with the 

 earth's surface." 



"The shear zone: When a fault is made up of a number of 

 slips on closely spaced surfaces, the section of the earth's crust con- 

 taining these minor faults is called 'shear zone.' This name would 

 also apply to the brecciated zone, which characterizes some faults." 



"A horse is a mass of rock broken from one wall and caught be- 

 tween the walls of the fault. (Fig. 193a.) 



