10 . Barrett — Movements of the Strand Line 



shore lines of the terraces give the maximum elevations, 

 the five Pliocene terraces reaching approximately to 1380, 1140, 

 920, 730 and 520 feet respectively. The Pleistocene terraces 

 below were, in comparison, very imperfectly developed, but 

 planation can be traced at stages whose mean elevations on 

 their inner margins are 360, 220, and 100 feet. That at 220 feet 

 is best developed, but none show the clear character of the 

 Pleistocene terraces farther south on the coastal plain, since 

 the Connecticut terraces were developed on formations of 

 resistant rock. Furthermore, all are older than the last glacia- 

 tion and have been obscured by that event. Their narrow 

 breadth and originally imperfect development in comparison 

 with the older and higher terraces appears to be a measure of 

 an acceleration of the diastrophic rhythm in Pleistocene time. 

 This crustal unrest is continued to the present; the present is 

 diastrophically as well as climatically a part of the Pleistocene. 



The broader Tertiary rhythm shown by the wide terraces 

 facing the sea must be complicated in the Pleistocene by the 

 special effects of the weight of the ice sheets, the changes in 

 volume of ocean water related to glaciation, and the percep- 

 tion of the briefer minor diastrophic movements whose records 

 are lost to sight among the larger movements of the past. 

 These complications do not hide the facts, however, which lead 

 to the conclusion that an abnormal crustal unrest beginning in 

 the Pliocene has marked especially the entire Pleistocene 

 period. The record which has been described shows the 

 rhythmic oscillation during the upwarping and emergence of 

 the Atlantic shore of the United States between latitudes 38 

 and 43 degrees. The record is different on the Pacific shores. 

 There it is doubtless more largely related to the orogenic forces 

 existent in latest times in the Pacific mountain system. On 

 the eastern shore the deposits older than the Pliocene show a 

 seaward tilt, greater for each older formation. This is a mark 

 of progressive crustal warping. For the Pliocene and Pleisto- 

 cene levels this warping, however, diminishes progressively. 

 These later changes are more largely broad and parallel move- 

 ments of level. They represent apparently more largely 

 movements of the sea itself. To what extent, however, the 

 net result is due to local movements of the crust cannot be 

 determined until the series of strand lines has been studied on 

 many shores and their resemblances and differences compared. 



These high-level terraces represent the height of successive 

 submergences. Let attention be turned next to the other side 

 of the rhythm, that of the record of emergences, as shown by 

 river valleys which now are drowned. Reaching far back into 

 the Pliocene each shore line is found to be marked by large 

 embayinents developed upon regions of softer rocks. The 



