THE EARTH. 57 



sion from the deep. The heat of the sun is very 

 probably a principal cause ; but it is not right to 

 ascribe to one only, what we find may be the 

 result of many. Earthquakes, severe frosts, burst- 

 ing waters, and storms tearing up the roots of 

 trees, have, in our own times, produced them ; 

 and to this variety of causes we must, at present, 

 be content to assign those that have happened 

 before we had opportunities for observation. 



CHAPTER VII. 



OF CAVES AND SUBTERRANEOUS PASSAGES THAT SINK, 

 BUT NOT PERPENDICULARLY, INTO THE EARTH. 



IN surveying the subterranean wonders of the 

 globe, besides those fissures that descend perpen- 

 dicularly, we frequently find others that descend 

 but a little way, and then spread themselves often 

 to a great extent below the surface. Many of 

 these caverns, it must be confessed, may be the 

 production of art and human industry ; retreats 

 made to protect the oppressed, or shelter the 

 spoiler. The famous labyrinth of Candia, for in- 

 .stance, is supposed to be entirely the work of 

 art. M. Tournefort assures us, that it bears the 

 impression of human industry, and that great 

 pains have been bestowed upon its formation. 

 The stone quarry of Maestricht is evidently made 

 by labour : carts enter at its mouth, and load 

 within, then return and discharge their freight 



