SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. g 



the material in which it was imbedded being easily recogniz- 

 able, it would have been referred to the Quaternary. We will 

 go still further back in its history. The tooth was nearly per- 

 fect and had been but little worn, showing that it had not been 

 shed during the lifetime of the animal, and not being connected 

 with any other portion of the skeleton, it may have belonged to 

 an animal of the Miocene Period, whose remains were imbedded 

 in the deposits of that period, and had been exposed and sub- 

 sequently separated from the other portions of the skeletion by 

 the action of the elements and again deposited in one of the 

 ''Dead Rivers" of the Pliocene Period, to be again disentombed 

 and removed after the lapse of many thousands of years. 



Had this tooth been covered up and left where the writer 

 found it (in close proximity to an Indian Rancheria), it might 

 after other thousands of years, have been discovered by some 

 future scientist and been considered satisfactory proof of the 

 contemporaneity of man and the Mastodon. 



Such instances show the necessity of close study, careful dis- 

 crimination and conservative deductions in an attempt to read 

 detailed history from the Book of Nature. 



THE LENGTH OF GEOLOGTC TIME. 



For the benefit of those who have not given much thought to 

 the subject of the Earth's age the following estimates made by 

 eminent geologists and physicists are given. Those of the 

 geologists are based upon the present rate of deposit of marine 

 sediment, and the destruction of land by erosion and denuda- 

 tion, compared with the total thickness of sedimentary rocks. 

 The correctness of the estimates — provided that tlie rates have 

 been always uniform^^is evident, but in the absence of that 

 assurance the conclusions are uncertain and elusive. 



The estimates of the physicists are based upon the application 

 of the laws of heat radiation, and their conclusions have ma- 

 terially modified the former theory, that for the deposition or 

 formation of the sedimentary rocks a minimum of hundreds of 

 millions of years were required, and for the time which elapsed 

 since the earth was in a molten state no limit could be given. 



Mr. Clarence King, a former United States Geologist, as the 

 result of experiments upon the behavior of certain rocks under 

 conditions of heat and pressure, came to the conclusion that it 

 cannot be more than twenty-four million years since the earth 

 was in a molten state or condition. 



Mr, Warren Upham gives forty-eight million years as the 

 age of the stratified rocks and one hundred million of years as 

 the age of the ocean. 



Sir Charles Lyell, the eminent English geologist, gave as his 

 estimate of the age of the fossil bearing sedimentary rocks, two 

 hundred and forty millions of years. 



