HABITS OF THE GREAT SOUTHERN TORTOISE. 41 



to tlie depth of several feet by the burrowing of these animals 

 that no trace of this original structure is shown in the railway 

 and other cuts except where by a rare chance the section is so 

 deep that it penetrates below the level of their migrations. At 

 first sight I was greatly puzzled to find that the superficial sands 

 of Florida, which have evidently been deposited beneath the sea, 

 exhibited no trace of stratification, which is invariably brought 

 about in deposits formed in shallow waters subjected to a strong 

 current action. It was only when I came to reckon on the influ- 

 ence of these creatures in destroying the original planes of strati- 

 fication that the riddle became plain. So far as I am aware, this 

 is the only case in which a burrowing animal has done so much 

 work as practically to efface the stratification planes in a wide 

 field of sedimentary deposits. It appears to me likely that the 

 absence of fossil remains in these superficial sands of Florida 

 may be explained by the endless stirring of the beds which these 

 creatures have effected. It is evident that in their motion 

 through their underground ways they have exercised a very con- 

 siderable degree of violence. A fossil which might have re- 

 mained well preserved in undisturbed beds would, from repeated 

 contact with the strong claws of the gopher, have been broken into 

 fine bits, and made ready to pass into the state of solution. As is 

 well known, ordinary marine fossils deposited in porous sands soon 

 become very frail, and would certainly not resist any such rude 

 treatment as they must again and again have received at the 

 hands of these animals. The railway and cliff sections of Florida, 

 which afford us the only opportunities for a careful examination 

 of the superficial sands, are in positions where they are accessible 

 to the gophers. In an examination of a good many miles of these 

 escarpments, I found only one or two points in which a trace of 

 the original bedding appeared to be distinguishable. It is evi- 

 dently difficult to account for the unstratified as well as the 

 non-fossiliferous nature of this deposit in Florida without some 

 such explanation as that to which our study of the gophers 

 leads us. 



To the student who wishes to ascertain the limits of evolution 

 under the influence of natural selection, the gophers present cer- 

 tain facts of great interest. It is evident, from the foregoing state- 

 ments, that the habits of this creature are eminently joeculiar, and 

 yet there are no manifest modifications of the body which fit its 

 peculiar needs. In shape the animal does not differ in any im- 

 portant Avay from our ordinary terrestrial species of Testudinafa, 

 which at most burrow in the earth for a little distance to secure 

 temporary concealment or protection from cold in the hibernating 

 season. All the most evident external modifications of the tor- 

 toise are directed to the end of securing protection against as- 



