OK THE A¥EST COAST 30'7 



zone^ thus giving what might be expected, an iiiterfingering of certain 

 elements of the three faunas. 



EOCE NE-MIO CENE RE LA TIO NSHIP,'^ 



Of the three Oligocene faunas, that of the Molopophorus lincolnensis 

 shows a closer relationship to the fauna of the Tejon (Upper Eocene). 

 A considerahle number of the species of the Molopophorus lincolnensis 

 zone are undoubtedly closely related to certain Tejon species. The 

 Eocene character is also shown in the close similarity of the generic as- 

 semblage. C. E. Weaver lias listed several highly ornamented gastropods 

 in the Molo])ophorus lincolnensis zone as common to the Tejon fauna. 

 On the other hand, the Agasoma acuminatum fauna, which is found in 

 deposits lower stratigraphically than that of the Molopophorus lincoln- 

 ensis zone, has nothing in common with that of the Tejon; its fauna is 

 more Miocene in character, so much so that when first described it was 

 considered to be of later Miocene*^ age than tlie Monterey (Lower Mio- 

 cene). The highest of the Oligocene faunas, that of the Acila gettysburg- 

 ensis zone, is also more closely related to the fauna of the Miocene than 

 to that of the Eocene. 



Undoubtedly these Miocene and Eocene relationships of the Oligocene 

 faunas, just pointed out, are very largely the result of differences of tem- 

 perature conditions. During Tejon periods tropical conditions prevailed 

 and the tropical marine faunas held sway well up into northern waters. 

 The Agasoma acuminatum fauna, which follows that of the Tejon, repre- 

 sents more temperate conditions of deposition. The Eocene representa- 

 tives of this fauna very probably were living during the Eocene period 

 in the region of the Arctic Circle. Following this the waters, at least 

 locally, as shown by the character of the fauna of the Molopophorus lin- 

 colnensis zone, were again much warmer and tropical species replaced the 

 temperate forms, to be later replaced by a more temperate fauna during 

 the deposition of the beds of the Acila gettysburgensis zone. At the 

 present time we can not say for a certainty that the Oligocene fauna 

 everywhere followed in the sequence as outlined above. As has already 

 been stated, it is still an open question whether the Agasoma acuminatum 

 fauna and that of the Molopophorus lincolnensis zone belong to distinct 

 horizons, the Oligocene opening with temperate conditions, later to be 

 followed by tropical, or whether these two faunas were contemporaneous, 

 the differences in temperature being local and the two faunas living in 



" J. C. MeiTiara : Note on two Tertiary faunas from the rocks of southern coast of 

 Vancouver Island. T'niv. of California I*ubl. Bull. Dept. Geol., vol. 2, no. 3, 189G, pp. 



lo^lo8. 



