THE EARTH THE ABODE OF LIFE 



miles in measurement. Consequently it will be seen that 

 the porous volcanic rocks with which the young earth was 

 covered contained all the materials for water-manufacture 

 within themselves. As the water began to form, squeezed 

 out of the porous rocks as we can squeeze it out of a 

 sponge (or as we might steam it out if we put the moist 

 sponge in an oven), it gathered itself into reservoirs 

 underground. As it increased in bulk it rose nearer to 

 the surface ; because, of course, owing to the heat of the 

 inner portions of the earth it could never succeed in 

 sinking below a certain depth. Doubtless it first ap- 

 peared at the bottom of the pits which had been sunk by 

 volcanoes or volcanic action. There must have been in- 

 numerable depressions in the earth's surface as widespread 

 and deeper than those which we can perceive on the 

 rugged surface of the Moon. We may gain an idea on a 

 very minute scale of what the first pits of water were 

 like from the examples (formed, however, at a much later 

 period and probably in a different way) of the crater lakes 

 that are left to-day. Some curious examples of " crater 

 lakes " are to be found in the Eifel district of Germany, 

 an ancient volcanic region which lies in the triangle 

 formed by the junction of the Rhine and the Moselle at 

 Coblenz. One of the pleasing peculiarities of this district 

 is that, owing to the volcanic nature of the soil, the 

 neighbourhood is seldom dusty, even in August or Sep- 

 tember, after the dry continental summer. It is well 

 worth visiting for its castles as well as for its crater lakes 

 and other volcanic relics, and it is the scene of R. L. 

 Stevenson's romance Prince Otto. The chief crater 



109 



