254 PHYSICAL GEOGRAPHY. 



by J. W. Lovering, assistant engineer. At North Conway, this series 

 connects with that of the Portland & Ogdensbnrg Railroad, with which 

 it closely agrees ; and the remainder of this line, which here turns north- 

 westerly, has been supplied by John F. Anderson, chief engineer, from 

 the surveys of that railroad, now being built through the White Moun- 

 tain notch. The whole line of this road is given from Portland, and, as the 

 reference of these surveys was to mean low water in Casco bay, as estab- 

 lished by engineers of the U. S. C. S., 4 feet have been subtracted from 

 the heights of their profile given in our annual report for the year 1871, 

 to reduce to mean tide. The connection between this series at Dalton 

 and the line along Connecticut river has been already mentioned. It 

 will thus be seen that the accuracy of this reference line is confirmed by 

 a close agreement of altitudes, obtained by five different courses of 

 direct levelling from the sea. 



A summary of prominent points along this line is as follows : 



Difference. Altitude. 



South Lawrence, Mass., depot, 49 



Exeter, +9 58 



Dover, +14 72 



Great Falls, +106 178 



Rochester, +48 226 



Lake Winnipiseogee, low to high water, ...... 496-502 



North Conway, P., Gt. F. & C. Railroad depot, .... 516 



White Mountain notch, railroad summit, 1893; surface, . . 1914 

 Connecticut river, one fourth mile below mouth of John's river, at 



head of Fifteen-mile falls, low to high water, .... 827.6-832 



Additional Railroad Surveys. 



Many other extended series of altitudes have been determined by the 

 various railroad surveys throughout the state, and wherever these have 

 been preserved and are still attainable, they have been secured, and are 

 presented in the tables following those of the special reference lines along 

 our east and west borders already described. In some instances, how- 

 ever, these records, from various causes, have been unfortunately lost. 

 On this account it was found necessary, in establishing our western 

 reference line, to level along our whole western boundary, although rail- 

 road lines extend over three fourths of this distance, and were adopted 



