which is now going on — so we know 

 how it is done. This is the wa)' in 

 which it takes place: The air and the 

 rains and the water in the ground act 

 upon the rocks, and cause them to 

 soften and fall to pieces, forming soils, 

 or sand, or little rock fragments. This 

 material is gradually washed away by 

 rains and floods. This does not usually 

 quite keep pace with the softening; so 

 the surface is covered with soil and 

 other loose material. But it is little by 

 little washed away, and carried down 

 to sea, where it settles on the bottom, 

 and forms layers of mud or of sand. 

 The mud afterwards hardens, and be- 

 comes a kind of rock known as shale. 

 The sands become cemented by lime or 

 iron, or some other substance, and form 

 a sandstone. The lime in the rocks 

 that softened and decayed is chiefly 

 dissolved out by the carbonic acid in 

 the waters of the ground, and is carried 

 away to the sea in solution. This lime 

 is then taken up by sea animals to form 

 their shells, skeletons, teeth, and other 

 hard parts. Afterwards the animals 

 die, and these hard, limy parts usually 

 crumble more or less and form a bed of 

 lime material, and later this hardens 

 into limestone. 



Some of the lime is also separated 

 from the waters by evaporation or by 

 other changes. You have noticed that 

 on the inside of a tea kettle there gath- 

 ers a stony crust. This is made of the 

 same material as limestone — indeed, it 

 is limestone. It was dissolved in the 

 water put in the tea kettle, but as the 

 water was heated and partly changed 

 into steam it could no longer hold all 

 the lime, and some or all of it had to 

 be deposited. So, in a similar way, sea- 

 water is dried up by the sun and air, 

 and deposits lime, and so beds of lime- 

 stone are formed. You will readily see 

 from what has been said why shales. 



sandstones, and limestones take the 

 form of beds lying upon each other. 



Now, away back towards the begin- 

 ning, when the ocean was first formed, 

 and some part of the earth was pushed 

 up so as to form land, this process be- 

 gan, and has been at work ever since. 

 The surface of the land has been moist- 

 ened by the air and moisture, and then 

 has been washed away to the ocean and 

 laid down in beds. When these grew 

 thick, and were pressed by the weight of 

 the newer beds that were laid down on 

 them, they hardened into rock again. 

 And this has gone on for a very, very 

 long time, and the beds of sandstone, 

 shale, and limestone so formed have 

 come to be many thousand feet thick in 

 some places. The land would all have 

 been worn away down to the level of 

 the sea if the earth had not kept shrink- 

 ing and wrinkling, or pushing up in 

 places. 



At different times portions of what 

 was once the ocean bottom have been 

 lifted and have become land. If these 

 beds are examined they will be found 

 to contain shells and corals and other 

 sea animals which were buried in them 

 when they were forming, and thus it is 

 known that they were laid down under 

 the sea. It is found also that the lower 

 beds contain kinds of life different from 

 those above, and the lower beds were, 

 of course, formed first. So, by studying 

 the sea-shells and other relics in the 

 beds, from the lowest ones up to the 

 highest ones in the order in which they 

 were formed, the various kinds of life 

 that have lived in the sea from the be- 

 ginning are found out. The life at the 

 beginning was simpler than it is now, 

 and quite different in many respects. 

 There were gradual changes from time 

 to time, and many strange creatures 

 appeared that do not live at present. 



