CLASSIFICATION OF SPRINGS 



545 



Four classes of springs in this group are distinguished in the 

 following paragraphs. 



WTiere the overlying material is thick and of wide extent, the 

 contact is ordinarily an unconformity. The irregularities of such a 

 contact are of minor significance, and here all the t}^es of springs 

 included in the previous group — gravity, inclined gravity, cuesta, 

 and mesa springs — may occur. The springs will be found at the 



o Sea level 



Fig. II. — Cross-section showing inclined hardpan on the north side of the West 

 Hills, Long Island, New York, and source of Mountain Mist Springs. (After Veatch.) 



lowest parts of the contact. Mesa springs that fulfil' these condi- 

 tions occur at the Hopi Buttes, in Arizona (Fig. 12), where the 

 overlying bed is a porous and jointed lava flow underlain by 

 patches of volcanic ash and the underlying impervious beds are 

 tUted and eroded shales and sandstones. The unconformity is 

 fairly smooth, but springs issue in the lowest places.^ 



Where the overlying porous material is localized and the 

 contact is irregular, the resulting springs may be called pocket 

 springs, because the reservoir from which the water is drawn lies 



' H. E. Gregory, op. cit., p. 139. 



