1 82 STUDIES FOR STUDENTS 



forces into components parallel to their strike and dip at any 

 given point, and thus the axes of these minor plications would 

 correspond to the local directions of greater and less thrust. 



Mo7ioclinal anticlines and synclines.- — -In regions of close mono- 

 clinal folds, the axial planes of which have a low dip, and espe- 

 cially if there be a little fanning, it may be difificult to discriminate 

 between anticlines and synclines. This principle is well illustrated 

 by the relations of the limestone and schist in the Housatonic 



Valley. The Stockbridge limestone composes the lowlands for 

 the most part. Rising from the lowlands are numerous schist 

 ridges, varying from small hills to mountains such as Tom Ball and 

 Lenox, the summits of which are from several hundred to a thou- 

 sand or more feet above the valley. These schist ridges are, in 

 fact, synclines which rest upon the limestone. However, obser- 

 vations of the dip across the ridge would in many cases lead to the 

 conclusion that they are anticlines, as upon opposite sides of the 

 ridge there is a divergence downward in the dip (Fig. i). Of 

 course dip of bedding is here meant, — not dip of schistosity, 

 which, while variable, dips with considerable regularity to the 

 east. This anticlinal appearance is well illustrated by the hill 

 called Turnip Rock and the larger hill known as Barack M'Teth, 

 and also by Tom Ball, all in, or partly in, the area covered by 

 the Sheffield topographic sheet of Massachusetts. In each of 



