Page:Popular Science Monthly Volume 34.djvu/51

Rh to the 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 influence of these creatures in destroying the original planes of stratification 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 considerable degree of violence. A fossil which might have remained 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 evidently 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 certain facts of great interest. It is evident, from the foregoing statements, that the habits of this creature are eminently peculiar, and yet there are no manifest modifications of the body which fit its peculiar needs. In shape the animal does not differ in any important way from our ordinary terrestrial species of Testudinata, 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 tortoise are directed to the end of securing protection against