SPRINGS. 



155 



tlie Avater to tnh along its upper plane until the formation somewhere comes to the 

 surface and with it the collected water of the spring. These conditions are illustrated 

 in the aeccompanyiug cut (Fig. 62), in which h c d of represents the upper fissured 

 formations through which the rain and suow waters penetrate to the lower imper- 

 meable strata below the line bf, necessarily gravitating to point/, where the oppor- 

 tunity for discharging as a spring exists; a smaller spring might occur at c. Such 

 conditions exist where lime or dolomite rocks overlie hard sandstones, compact clay 



Fig. 62, — Fissure spring. 



slates, or clay beds. These springs, as a rule, are much less dependent on the changes 

 of precipitation and temperature; they are mostly continuous and even in their flow 

 and their temperature. 



The third class of the running springs may properly be called "cavern" springs, 

 from the fact that while their waters are drained like those of the second class, they 

 aie first c(dlected in some subterranean basins or caverns, and appear on the surface 

 as overflow of these basius. 



In the accompanying figure (63), a h c is the catchment basin, from which the vari- 

 ous fissures conduct the water to A, overflowing at X into B, and from there over- 

 flowing and appearing at the surface at Y. 



Fig. 63. — Cavern .spring. 



This kind of spring is found frequently in limestone formations, and since the 

 waters of such often come from great distances from above their discharge at the sur- 

 face, they are usually of very cold and even temperature; they are ;ipt to run low 

 "when the soil is frozen and when precipitation is small; and their discharge is more 

 or less intermittent. The (tbstruction of the old and ope.iing of a new outlet by a 

 fall of rocks at A' and V, and the widening of a fm-merly insignificant fissure at- or t, 

 may reduce the flow or 8toi» the original spring entirely, opening a new one in an 

 entirely difl'ereut part of the locality. 



