SUBTERRANEAN SPRINGS. 219 



river, and when, from long continued rains, or frem melting of 

 snows and ice, the brooks and tributary streams are swollen, a 

 flood of water is poured down to the ocean, which bears with it 

 ijaaterials transported a thousand miles, and in quantities of which 

 we can form little conception. The water, which falls upon the 

 surface of the earth and penetrates its upper soil, and is thus pro- 

 tected from evaporation, descends lower and lower, until it meets 

 some impervious bed of clay, or marl ; here it accumulates and 

 forms a hidden pond, and slowly undermines whole tracts "of 

 country, and in the course of ages subterranean rivers are formed. 

 The various mineral ingredients dissolved in water, are borne 

 up by springs, and again flowing over or through the porous sands, 

 form limestones, sandstones, and ironstones; and thus continu- 

 allv the process is going on. 



The action of all springs, and running waters, is to level the 

 surface of the earth. The streams, which always flow from an 

 elevated source, bear down the disintegrated portions of moun- 

 tains and hills, and tend continually to fill up the bed of the sea. 

 Unless a counterbalancing cause existed, and the elevation was 

 made to compensate this continual degradation or levelling, the 

 whole dry. land would ultimately disappear. We find in earth- 

 quakes and other volcanic effects the elevating power ; and al- 

 though, as we shall presently show, the sea may gradually en- 

 croach upon the shores of one country, yet the lands of another 

 will be gradually upheaved, and something like a balance will be 

 maintained. Minute therefore as are the transmutations which 

 are going on continually around us, and by which, long since, in 

 the same quiet manner, the leaf that floated down the stream, a 

 thousand years ago, and the insect that dropped into water, have 

 been incrusted, and preserved with a fidelity which mocks the 

 sculptor's art, yet we see that processes like these, have 



" Turned the ocean -bed to rock, 

 And changed its myriad living swarms 

 To the marble's veined forms." 



" How marvellous" observes Sir Humphry Davy, " are those 

 laws by which even the humblest types of organic existence are 



