34 THEORJ OF THE EARTH. 



of the level would be a matter of so much in- 

 terest, and where fixed and ancient works afford 

 so many means of measuring its variations, the 

 mean level of the sea is constant. There has, 

 therefore, never been a universal lowering, nor a 

 universal encroachment, of the waters of the ocean. 

 In some places, indeed, such as Scotland, and va- 

 rious parts of the Mediterranean, evidence has 

 been thought to have been found, that the sea 

 has risen, and that it now covers shores which 

 were formerly above its level *. 



Volcanoes. 



The action of volcanoes is still more limited, and 

 more local, than any of those which have yet been 

 mentioned. Although we have no precise idea of 

 the means by which nature keeps up these violent 

 fires at such great depths, we can judge decided- 

 ly, by their effects, of the changes which they may 



* Mr Stevenson, in his observations upon the bed of the 

 German Ocean and British Channel, maintains that the level 

 of the sea is continually rising, and has been very sensibly 

 elevated within the last three centuries. Fortis asserts the 

 same of some parts of the Adriatic sea. But the example 

 of the Temple of Serapis, near Pouzzola, proves that the 

 margins of that sea are, in many places, of such a nature as 

 to be subject to local risings and fallings. On the other 

 hand, there are thousands of quays, roads, and other works, 

 made along the sea-side by the Romans, from Alexandria to 

 Belgium, the relative level of which has never varied. 

 Note K. 



