152 University of California Publications in Geology [Vol. 7 



Introduction 



The Pleistocene rodents described in the following paper were 

 obtained from Potter Creek Cave and Samwel Cave on the 

 McCloud River, Shasta County, California, and from the asphalt 

 deposits at Rancho La Brea, near Los Angeles, California. The 

 specimens are all from the palaeontological collections of the 

 University of California. 



Potter Creek Cave has already been fully described and a list 

 of the species found in it given by W. J. Sinclair; 1 a brief 

 description of Samwel Cave is furnished by E. L. Furlong; 2 

 while a discussion of the Rancho La Brea beds has been pub- 

 lished by J. C. Merriam, 3 so that any detailed description of the 

 three localities seems unnecessary. The caves were formed along 

 fissures mainly by percolating water removing limestone in solu- 

 tion and not by the action of streams. The rodent remains of the 

 caves are found in strata of clay with gravel lenses, excavated 

 down to a depth of twenty-five feet, and they are very abund- 

 ant in places, especially those of Neotoma, a form which prob- 

 ably lived in the caves soon after they began to form. The bones of 

 many of the larger animals show evidence of having been gnawed 

 by rodents, and the tooth marks appear to be those of Neotoma. 

 Aplodontia, Thomomys, and Citellus, burrowing rodents, come 

 next in order of abundance. Lepus is quite common, a fact which 

 might be explained by presence of the lynx, which feeds so largely 

 on rabbits, and, living in caves, brought in its prey to be devoured. 

 The remains of other rodents which do not live under the ground 

 were doubtless washed into the caves by the seasonal rains. 



The asphalt deposits were formed from the surface accumu- 

 lation of tar in which animals were caught, and we find the num- 

 ber of rodents exceedingly small, in fact a minimum as compared 

 with the bones of carnivores. This is explained by the fact that 

 the latter were attracted to these pools by animals entangled in 

 the tar, and rodents would be caught only by straying acci- 

 dentally into the pools. 



1 Science, vol. 17, no. 435, pp. 708-712, 1903. 



2 Amer. Jour. Sc., Ser. 4, vol. 22, 1906, p. 235-247, 1906. 



3 Merriam, J. C, Mem. Univ. Calif., vol. 1, no. 2, 1911. 



