253 J. B. WOODWORTII APPALACHTAXS IX XEAV EXGLAXD 



there is, if the structure be understood by the writer, a pronounced west- 

 ward overturn of apparent folds, along the western side of Xarragansett 

 Bay from Providence southward. If, however, one adopt the view that 

 this section is not composed of isoclinal folds, then the beds may be re- 

 garded as simply dipping eastward into the basin. On the other hand, 

 the cross-section of Prudence Island shows a syncline with vertical beds 

 on its eastern side and only moderately steep dips on the western side. 

 Accordingly, the general structure of the Xarragansett area is somewhat 

 diverse and exhibits more of local control than of a general widespread 

 direction in the overturning of folds. 



Plax of the Sectioxs as a AYhole 



GEXERAL i<TA TEMEXT 



The impression one receives on the whole of these folded Carboniferous 

 strata of southeastern Massachusetts is against the idea of an overthrust 

 from the Atlantic border inward toward the central axis or western 

 border of Appalachian structure. The general direction of overturning 

 and overthrust is toAvard, rather than away from, the ocean basin on the 

 east and south. It is obvious that the Boston-Providence area is not a 

 part of the typical Appalachian folded structures along the western mar- 

 gin of Xew England and the States on the south, and from this limitation 

 it is inferred that maximum overthrust toward the Atlantic would be 

 found along the eastern side of this region : hence that somewhere in that 

 direction yet more pronounced southeastward overthrusting may have 

 taken place. 



The conventionalized view of the geological section across Massachu- 

 setts thus presents itself to us as one having a central tract of nearly flat- 

 lying crystalline schists, certainly as old as the Carboniferous and thought 

 by some to be yet older and probably of Precambrian age, to the east and 

 southeast of which there is a region of recognizable overthrusting toward 

 the Atlantic, while to the west of the schists overthrusting is to the west 

 and is of the Appalachian type. In this view the section presents a cen- 

 tral axis of little horizontal motion relative to the margins as they are 

 now shown. This central axis of least horizontal compression is highly 

 crystalline and must have been at one time under a thick cover of super- 

 incumbent rock, whatever be the age of the schists now at the surface. 

 If the rocks of this axis are of Carboniferous age, the surface of the Pre- 

 cambrian schists is presumably not far below, since the Carboniferous 

 here can not be very thick ; if, however, the schists now at the surface are 

 of Precambrian age, then the former Precambrian surface here rose dur- 



