STRUCTURAL FEATURES 



277 



tions on tin- Hanks of tin- larger, they are called gr<mti<-lines, or 

 antii'linoria (Figs. 219 and 255), and geosynclines or syndinoria 

 ( Fig. 256). Folding 

 may be accompan- 

 ied by the develop- 

 ment of slaty cleav- 

 age (p. 293). 



As found in the ^> - 2 5^ - Synclinorium, Mt. Greylock, Mass. (Dale, 



, , , U. S. Gcol. Surv.) 



field, most folds are 



much eroded, and in many cases completely truncated (Fig. 255). 

 The structure is then determined by a careful record of dips and 



strikes. On the field 

 | map, the record 



may be made as 

 I shown in Figs. 257 



and 259, where the 

 I free ends of the 

 I" lines with but one 



free end, point in 



-'57 



Fig. 260 



Fig. 259 



Fig. 2S 7. Map record of dip and strike,' showing the direction of dip, 

 vn. linal >t met ure. while the other lines 



Fig. 258. Diagram showing the structure correspond- represent the direc- 

 ing with Fig. 257, as seen in cross-section. f t 'I A 



Fig. 259. Map record of dip and strike showing l nKe - A P~ 



anticlinal structure. plying this method, 



Fig. 200. The structure of the area shown in Fig. 259, t h e structure Shown 

 in cross-section. 



in Fig. 257 repre- 

 sents a syncline, and that in Fig. 259 an anticline. In cross-section, 

 the structure represented by Fig. 257 is shown in Fig. 258; that 

 of Fig. 259, in Fig. 260. ^ j_ J_ J_ J_ ^/ 



Fig. 261 shows a doubly 

 pitching anticline; that is, 

 an anticline the axis of 

 which dips down at either 

 end. Fig. 262 shows a com- 

 bination of synclines and 

 anticlines, and Fig. 263 a 

 cross-section along the line 

 ab of Fig. 262. The out- 

 crops of rock where the dip and strike can be determined may be 

 few and far between, but when they are sufficiently near one 



v 



A < 



> T T T T A 



Fig. 261. Map record of dip and strike 

 showing plunging (dipping down at ends) 



anticline. 



