2i6 FRANCIS PARKER SHEPARD 



the exact times of these disturbances shows that out of 54 only 9 

 can be said with any certainty to have occurred at or very near 

 the division between the periods, and so far as can be told from the 

 rest they may have occurred well within one of two or even three 

 periods. Therefore the numerous disturbances may be taken as 

 well to indicate a continuous series of orogenic movements as an 

 intermittent series. 



Therefore the conception of periodic diastrophism should be 

 critically re-examined and the evidence sifted with care before it can 

 be used as an argument against continuous isostatic adjustment. 



