RIVER SYSTEMS OF NEW HAMPSHIRE. 317 



and wealth of the state. A general view of the nature of these resources 

 will cause us to see utility as well as beauty in our river and lake scenery. 



Among the physical characteristics of the state which affect the amount 

 and availability of its water-power, we should first consider its. geological 

 structure. Here the most noticeable feature in this relation is the ability 

 of the ledges to resist decomposition. This is the prevailing character of 

 very ancient rock formations. They resist the wearing action of water, 

 breaking the course of streams with numerous falls and abrupt rapids, 

 and maintaining the uneven condition of river beds, which renders water- 

 power capable of use. The importance of this feature will be rightly 

 estimated by a comparison with the prevailing form of river channel in 

 the south-western portion of the United States, where the rivers find 

 their way by an almost subterranean passage through canons many miles 

 in length and hundreds of feet deep, while the parched and sterile country 

 is rendered impassable by their yawning chasms. This character of our 

 rocks also reduces the amount of water, which is absorbed through crev- 

 ices and fissures in strata, and which, in a season of drouth, is lifted to 

 the surface, and burned away by evaporation. It is also of peculiar 

 importance in relation to the water-retaining capacity of our lakes and 

 ponds, these being in the majority of cases underlaid and walled in with 

 impervious rock. The same consideration insures the reliability of 

 artificial reservoirs wherever natural slopes of land admit of their con- 

 struction. 



It is also to be noticed that the disintegrated material, which almost 

 everywhere overlies the solid rock, is comparatively shallow. The sides 

 and bed of nearly all our streams, at points where falls or rapids exist, 

 are rock-set and rock-bound, though apparently covered with earth. 

 Ravages of river beds and diversions of river courses, which in alluvial 

 districts are productive of much inconvenience, or even of serious losses, 

 are on this account very rare. Canals and race-ways can be constructed 

 in permanent material, and when once completed need no repairs. Mills 

 and accompanying structures can be planted on ledge bottom, and thus 

 defy the treacherous undermining of deep currents. A permanent dam 

 can be built at almost any point where the slope of a stream is sufficient 

 to produce a rapid ; so that, dam succeeding dam, the whole descent of 

 the stream may be utilized, the damage from flowage or from wear upon 



