CLASSIFICATION OF SPRINGS 545. 



divided into two classes, one in which the overlying material is soft 

 and the other in which it is hard. Those of the first class may be 

 called inclined gravity springs (Fig. 9 a) and those of the second 

 cuesta springs, after the topographic feature analogous to a mesa. 

 (Fig. 9 h). Large springs of the inclined gravity type occur near 

 Baden-Baden, Germany (Fig. 10). At this place the lower and 

 middle Buntsandstein, both porous and water-bearing, rest on the 

 smooth erosion surface of the granite. The sandstone has been, 

 tilted and eroded into isolated patches. Numerous springs issue 

 along the contact of the sandstone and the granite on the lower side 

 of these erosion remnants. A few springs occur in the talus slopes. 

 and on the higher contacts.^ 



Good examples of cuesta springs are those which arise at the^ 

 contact of basaltic lava and shales of Tertiary age along the western 

 flank of South Table Mountain, north of Oroville, California. The 

 lava is sufficiently jointed and porous to collect water, which runs 

 down the dip of the contact and emerges along the western and. 

 lower face of the cuesta. 



If the underlying bed is of small extent, springs can only occur- 

 where the impervious layer dips with the slope of the hillside but at 

 a smaller angle. These springs are essentially like those in which 

 the impervious layer is horizontal and may also be called hardpan 

 springs (Fig. 9 c) . The Mountain Mist Springs, in the West Hills,, 

 along the northern shore of Long Island (Fig. 11), are of this class. 

 The underlying hardpan is a compact till, and the j>erched water 

 table lies about 200 feet above the main water table.^ 



3. Springs at the outcrop of an irregular surface. — Where the 

 underlying impervious bed has an irregular surface, the overlying 

 material is commonly thin and unconsolidated — a mantle over- 

 lying the bed rock. In humid countries the great majority of 

 springs are formed by water that collects in the reservoirs afforded 

 by this porous material. It varies in thickness and character and 

 the irregularities of the underlying surface originate in diverse ways. 



^H. Eck, " Geognostische Beschreibung der Gegend von Baden-Baden, Rothen- 

 fels, Gernsbach, und Herrenalb," K.-preuss. geol. Landesanstalt Abh., neue Folge, 

 Heft 6 (1892), pp. 653 £f. 



^ A. C. Veatch, "Underground Water Resources of Long Island, N.Y.," U.S^ 

 Geol. Survey, Prof. Paper 44 (1906), pp. 57-58. 



