ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 69 



Doadmaii Island, aiul the otlier from tlie Pleistocene (upper San Pedro series) at 

 Spanish Bight, San Diego. The nearly total absence of this species from even the 

 Pleistocene dejiosits is accounted for by the length of time it would take the species 

 to migrate to the California coast from Alaskan waters, where it first reached the 

 American shore during Pliocene or earlj- Pleistocene times. This scarcity of the 

 Haliotuhc, which are so common in the living fauna, in even the upper San Pedro 

 deposits, is more evidence in favor of the theory that a long period of time has elapsed 

 since the deposition of the upper San Pedro series. 



Dr. J. P. Smith explains the phenomena of the similarity of the late Tertiary 

 and early Pleistocene fauna, and the somewhat similar, though diverging, living faunas 

 in this way: during Tertiary time there was an elevation of the submarine shelf 

 which follows the line of the Aleutian Islands. This elevation made possible the 

 intermigration of many species which otherwise never could have crossed the abyssal 

 gap which now separates the northwestern American and Japanese regions. After 

 the elevation of this shelf it remained in a more or less constant position for some 

 time, and then became deeply submerged again, with a consequent breaking of the 

 faunal connection between the two regions. 



From the evidence brought forward in this paper, it has been seen that the 

 late Pliocene and early Pleistocene was a period of the southward extension of boreal 

 conditions on the west American coast; it would, therefore, be natural to infer that 

 approximately the same conditions prevalent on the Californian coast during late 

 Pliocene times also prevailed along the Japanese coasts during the same period. A 

 detailed study of the Tertiary and Pleistocene deposits of Japan is awaited with 

 interest, as such a study will throw more light on the conditions prevailing on the 

 shores of the North Pacific during the later geologic epochs. 



