SPRINGS 17 



Seepage springs may emerge along the top of an underlying 

 impervious bed, but more commonly they occur where valleys are 

 cut downward into the zone of saturation of a more or less uni- 

 form water-bearing deposit. Under favorable conditions the seep- 

 age from sands, as on Long Island, New York, gathers into 

 channels and forms streams of considerable size, some of them 

 flowing 5,000,000 gallons or more daily. 



Seepage springs, as in the cases cited, are commonly of the 

 gravity type, but where channels or fissures emerge beneath beds 

 of sand or gravel seepages not infrequently result from true arte- 

 sian springs. 



Tubular Springs. --Tubular springs embrace a great variety 

 of flows, including both those in the small more or less tubular 

 passages in the drift and those occupying large solution channels 

 or caverns in the soluble rocks. 



The channels of springs in the drift are generally established 

 along some more or less sandy or other porous layer, or perhaps 

 along the path left by a decaying root. The motion at first ap- 

 pears to have been mainly that of seepage, but in many springs a 

 passageway has been gradually opened, along which a definite 

 stream finds its way. The waters reach the channels by percolation 

 through the clays and sands and are usually free from pollution 

 except when near cesspools or vaults sunk some distance into the 

 ground. 



In limestones and other soluble rocks the underground pas- 

 sages may reach many miles in length. Single passages, as in the 

 Mammoth Cave of Kentucky, have been traversed for a distance 

 of many miles, and passages several times as long, though as 

 yet undiscovered, probably exist. Some of these passages are 

 many feet in diameter and are traversed by streams of considerable 

 size, or even by rivers. The Silver Springs of Florida give rise to 

 a river which is navigable from the ocean to its source in the 

 springs, and springs of similar volume occur at other points in 

 Florida and Arkansas and possibly elsewhere. The waters of 

 such springs vary greatly in composition, although most of them 



