568 



SCIENTIFIC RECREATIONS. 



\ 



who wishes to pursue the study for himself. We will endeavour so to put 

 the features of the stones and rocks before him that they will be recognized 

 by the passer by. We will try to show how the earth has been built up, 

 and how the great and terrible changes through which our little globe has 

 passed have been effected. In our own islands, Great Britain and Ireland, 

 we shall find traces of all the materials likely to be useful to us in our quest, 

 As has been well said, " Geology is the Physical Geography of the past." 



CONSTITUTION OF THE EARTH. 



The descent from rocks to stones, from stones to gravel, from gravel 



to sand, is evident to everyone, so we need 

 not insist upon the fact that sand is pow- 

 dered rock, and that an aggregation of sand 

 particles makes stones. We have heard in 

 the Mineralogy section that there are certain 

 " earths" silica, alumina, lime, etc. Of 

 these " earths," the two former constitute the 

 greater portion of the ROCKS. Lime, also, is 

 very evident, and in limestones fossils or 

 organic remains are abundant. Now we 

 must entirely put away from our minds the 

 old idea that the earth we live on was created 

 at once, or as it appeared to the first human 



beings. Our planet was prepared for man by degrees during millions of 



years. We conclude that the earth was originally composed of certain 



elements, and we find the same ele- 



ments in the sun. Therefore, sup- 



posing (as is supposed) that the earth 



came from the sun, we have all the 



material of the globe in a fused 



state. As the earth cooled, rocks 



were formed by pressure, and then 



water came, and now we can read 



" books in the running brooks, and 



sermons in stones" at our leisure. 

 Perhaps as someone reads this 



he may be walking by the sea- 



shore kicking the pebbles or seated 



upon the sands, the grains of which 



are so very tiny. He will probably 



find sand, shingle, and gravel with- 



in reach, and perhaps the curious- 



looking "pudding stone." Now 



what can we learn from these stones 



Fig 639. Shells in chalk. 



slreamlet . 



