ALTITUDES. 249 



engineer's level. These being employed as starting-points for compara- 

 tively short series of barometrical levels, the latter will be perfectly 

 reliable, so far as regards the accurate construction of profiles across the 

 state, or the delineation of contour lines on a map. For these transverse 

 series, railroad profiles have been employed whenever attainable, together 

 with surveys for canals, water-works, &c., gaps in series being filled up, 

 and a large amount of necessary extensions made. As part of this work, 

 it will be seen that a continuous series of actual levelling has been per- 

 formed under the direction of the geological survey along our entire 

 western boundary from Massachusetts to Connecticut lake. 



Exact information upon this subject, now for the first time obtained 

 throughout the entire extent of New Hampshire, as here given in tabular 

 form, and as presented to the eye in the profiles of geological sections in 

 the state museum, and which it is intended to put in a still more practical 

 shape in a raised map of New Hampshire, may be said to be in many 

 respects of not less importance than a correct outline of the boundaries 

 of the state, with its division into counties and townships. It will be 

 readily seen that knowledge of this kind is almost indispensable to the 

 geologist. Beyond this, when considered in connection with geological 

 structure and proximity to the sea, the relative elevation of any area is 

 the determining feature upon which depend the character of its climate, 

 its agricultural products, its forest trees, the amount and location of its 

 water-power, the facilities for communication, and the consequent distri- 

 bution of population and wealth. 



The different series of altitudes measured by actual levelling are first 

 given, nearly all of which are put in heavy type to indicate their superior 

 reliability, having been proved correct by the agreement of results 

 obtained along different routes. In the lists of altitudes which fol- 

 low these, the same heavy type designates such points as belong to 

 these series, or have otherwise been exactly determined. Altitudes given 

 in ordinary type have been obtained either from levelling, where some 

 discrepancy when connected with more carefully determined series pre- 

 vents a confidence in their entire correctness, or, as in the sections across 

 the state, from barometrical measurement ; all of these are to be regarded 

 as closely approximate. 



This method of printing, and the particular description of the way in 

 VOL. i. 34 



