CH. XL. PETROLOGY. 455 



England, Denmark, Germany, America, and indeed in almost 

 all countries. 



It is impossible, without a knowledge of geology, to 

 realise how very long ago these last-mentioned men must 

 have lived. For a long time we had only their tools, or a 

 few doubtful skulls and bones to prove their existence, but 

 in 1886 two human skeletons which were found in a cave 

 in the province of Namur in Belgium, together with ex- 

 tinct animals, have taught us more about them. These 

 skeletons represent thick-set clumsy men of a very low type, 

 agreeing well with the other parts of skeletons which 

 had been previously found. Their tools were rough and 

 unpolished, and the bones of the mammoth, rhinoceros, 

 cave-bear, and cave-hyena, lie buried with them. Since 

 these men lived and their remains were buried in the rocks, 

 there has been time for beds of immense thickness to be 

 laid down little by little, as the Ganges is laying them down 

 now; for parts of the French valleys to be gradually washed 

 away, and their shape altered ; for rivers to change their 

 courses, and vast beds of peat to grow over the bottoms of 

 the valleys ; and, more than all, for whole races of animals 

 which once lived to have died quite away from the face of 

 the earth. These facts give some idea of the long ages 

 that man must have been upon our globe. 



Study of Petrology. For nearly a hundred years after 

 the time of Werner (p. 216) geologists were chiefly occupied 

 in studying the causes of change in the earth's surface, and 

 in its inhabitants, and the chronology of the different strata 

 as shown by fossil animals and plants. During this time, 

 though mineralogy was always taught, it did not form a 

 leading feature in geology as in the time of Werner. Of 

 late years, however, this has been altered. In 1827 

 William Nichol of Edinburgh discovered a method by 



