FORMATIONS AND PHYSICAL HISTORY 



353 



Cambrian beds, if truncated below the level of the bottom of these 

 beds at their highest point, exposes two belts of Cambrian strata, 

 one on either side of a pre-Cambrian axis, as represented in the 



Fig. 312. Diagram illustrating the relation of Cambrian formations, A, B, and 

 C, to older rocks. The diagram suggests that the Cambrian formations have been 

 eroded back from their original margins, A', B', and C'. 



Fig. 313. Diagram illustrating the general relations of Cambrian beds in the 

 interior. The Cambrian, - , is represented as appearing at the extremes of the 

 diagram, and as dipping below younger beds between. 



left-hand part of the figure. If the truncation is at a level below 

 the top and above the bottom of the Cambrian (right-hand side of 



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Fig. 314. Diagram showing the positions of outcrops determined by folds. 



Fig. 314), the strata of that system are exposed in a single belt along 

 thr axis of the fold. (3) In some places, Cambrian outcrops are 

 surrounded by older 

 formations. In such 

 cases the Cambrian 

 outcrops presuma- 

 bly represent rem- 

 nants which have Fig- 315- Figure to illustrate isolated occurrences of 

 escaped erosion Cambrian surrounded by older formations. 



They may occupy depressions in the surface of pre-Cambrian 

 formations, or may constitute hills (Fig. 315). 



