238 H. L. FAIRCHILD — PLEISTOCENE MARINE SUBMERGENCE 



The student of this subject will be able to use the chart for the discov- 

 ery and mapping of shore features, and the numbering is left open to per- 

 mit insertion of new data. 



In territory east or west of either valley some recognition should be 

 given to the variation of the isobases from the latitude parallels. It is 

 estimated that the variation in altitude going east or west is about 0.8 

 feet per mile ; this is to be deducted toward the west and added eastward. 

 In illustration of this variation two localities may be noted. Prof. 

 Joseph Barrell showed the writer a small but excellent delta at Westville, 

 a northwestern suburb of New Haven, the summit altitude of which ac- 

 cording to the map is 165 to 170 feet. This is about 15 feet low for the 

 same latitude on the Connecticut Eiver, but, being 18 miles west, is near 

 the theoretic height. Prof. H. E. Gregory pointed out the elegant sand 

 plains in the Naugatuck Valley at Seymour, Connecticut. The map alti- 

 tude is 160 to 180 feet. If we take 170 feet as the best figure, we find 

 it is about 20 feet under the datum plane for the latitude (41° 23') . Sey- 

 mour lies 22 miles west of Middletown, which makes the water level 17.6 

 feet lower. Of course these figures are not precise, but merely illustrate 

 the principle. 



COMPARISON OF DATA 



Taking the continental depression at Montreal as 520 feet Dana cal- 

 culated the rate of uplift as 1.5 to 1.25 feet per mile (volume 23, pages 

 197-198). On this basis he estimated the marine plane at several locali- 

 ties in the Connecticut Valley. The following table gives Dana's figures 

 for his marine plane and his river flood levels in comparison with what 

 is now regarded as the approximately true marine plane : 



