560 KIRK BRYAN 



b) Underlying bed is of small extent ; common in uncon- 

 solidated alluvium; impervious bed is usually clay, 

 cemented gravel, "mortar bed," caliche, or hardpan. 

 (i) Hardpan Springs. 



2. Impervious bed has an inclined and regular surface; all 

 springs on the low side unless the overlying bed is very 

 thick|and the dip low. 



a) Underlying bed is of large extent. 



(i) Inchned Gravity Springs. The overlying 



material is soft. 

 (2) Cuesta Springs. The overlying material 



is hard; of same character as mesa springs. 



b) Underlying bed is of small extent; as in hardpan 

 springs. 



(i) Impervious layer dips away from hill; 



spring possible. 

 (2) Impervious layer dips into hill; spring 



possible only in ravines. 



3. Impervious bed has irregular surface. 



a) Overlying porous material is thick and of wide 

 extent; contact is unconformity. Gravity, in- 

 clined gravity, mesa, and cuesta springs may 

 occur, but springs will be sharply localized at 

 lowest parts of contact. 



b) Pocket Springs. Overlying porous material is 

 unconsolidated and more or less discontinuous, 

 residual soil, talus, landslide debris, alluvium, till, 

 stratified drift, wind-blown sand, or volcanic ash. 



c) Overflow Springs. Irregular floor is not continu- 

 ous, but porous bed is saturated and overflows at 

 lateral contacts; common at receiving end of 

 artesian systems. 



d) Rock Dam Springs. Irregularities of the rock floor 

 under an alluvial plain force water to surface ; these 

 may be projections of floor of basin, projections of 

 partly consolidated older alluvium, igneous dikes, 

 or volcanic plugs. 



e) Fault Dam Springs. Dam caused by faulting. 



■C. Artesian Springs. Due to pervious bed between impervious 

 materials. 



1 . Dip Artesian Springs. More or less regularly bedded rocks ; 

 tilted porous bed crops out in valley; usually sedimentary, 

 also alternations of lava flows, flow breccias, tuffs, gravels. 



2. Siphon Artesian Springs. Similar rocks; folded and with 

 outcrops in valley. 



3. Unbedded Artesian Springs. Rocks not regularly bedded, 

 but mass of porous material is exposed so as to receive 

 water and crops out in valley; occur in till and perhaps in 

 other rocks. 



