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are to ascertain the age of the earth. Aji examination 

 of the several deposits that form the crust of the earth 

 shows that they are composed of certain vegetable and 

 animal productions, and having ascertained the rate 

 of growth of each, it may become a simple sum in addi- 

 tion to tell how old the earth is. An examination of the 

 delta of the Mississippi disclosed eleven different deposits 

 of trees, each of which were from six to eight hun- 

 dred years old, and each must have grown on the same 

 spot ; and yet they only composed a depth of not many feet. 

 Spine birds and animals have a very rapid growth, while 

 others are very slow. A speckled turtle, for instance, has 

 scarcely reached half its growth in eleven years. Prof. 

 Agassiz dwelt at length upon the importance and value at- 

 tached to the study of common things, The more we know 

 of Nature, the more suggestive she is. Like an old friend, 

 she opens her heart to us freely, if we seek a thorough ac- 

 quaintance with her. 



Prof. A. CROSBY of Salem, inquired whether the same 

 rule of classification spoken of in the case of snails would 

 apply to vertebrate animals. 



Prof. AGASSIZ said he had not fully investigated that 

 point. He had just set some children at work to catch all 

 the sculpins they could, in order that he might make the 

 test. He was of the opinion, however, tliat vertebrate ani- 

 mals of the same kind born at precisely the same period, 

 and living under precisely the same circumstances, would 

 all grow nearly to the same dimensions during the same 

 time. The difference in the size of human beings is in 

 a great measure owing to the different circumstances 

 under wliich they are born and live. He spoke of the great 



