Life of Surface Deposits. 155 



vidual, the length of its life or the time allotted 

 to its geological horizon, or the prodigious 

 numbers to which it reached, this great ele- 

 phant stands at the head of its column. In 

 its presence our living elephant is but a de- 

 generate offspring, indicating the rapid pass- 

 ing away of the race. There are scarcely any 

 fossil beds of this Surface division but have 

 their Mammoth teeth as trophies of their ex- 

 cavations. The Mammoth tooth is not sim- 

 ply a bulky mass, but an admirably con- 

 structed and complex piece of work. The 

 unit in its structure is simple, a single cusp. 

 The cusp is united with other cusps to form 

 a flat plate. The cusps are cemented together 

 by layers of dentine, each period of the ele- 

 phant's life being accorded a specific number 

 of plates so that the first molar, the milk 

 tooth, is cut at three months old and shed 

 when the calf is two years old; the second, of 

 eight or nine plates, is shed at six years; the 

 third, of eleven , thirteen plates, is shed at 

 nine years; the fourth, of fifteen or sixteen 

 plates, is shed at twenty-five years; the fifth, 



