22 STUDIES IN GEOLOGY, No. 3 



represent five per cent ; if collecting were sure to have been 

 strictly representative such figures might bear weight, 

 but such is rarely the case, and is not recognizable if it does 

 occur. It is obvious that the determination of affinities in 

 the case of a small fauna of doubtful or heterogeneous aspect 

 is attended by danger, and it is fortunate for the results of 

 the present study that the affinities of the Zorritos fauna are 

 strong enough to leave no doubt as to its age relative to the 

 known Antillean faunas, and little or no doubt as to its 

 position in the standard European time-scale. 



The accurate determination of the horizons from which 

 the fossils were taken offered a first-hand opportunity for the 

 discernment of differences in the faunal characteristics of 

 the three members of the Zorritos formation, and in view 

 of the superficially diiferent appearance of the fossils the 

 work was begun in anticipation of the discovery of faunal 

 zones, possibly of distinctly different ages. As will be seen 

 when the three faunas are taken up in detail, such difference 

 is by no means marked, and although the Upper Zorritos 

 may to some degree be differentiated from the Lower Zor- 

 ritos in age, the difference between the two faunas is probably 

 more one of facies than of time. The Variegated faunule is 

 too small to permit the drawing of conclusions further than 

 to indicate its relationship to the neighboring beds. 



Six of the eighty-one species are common to the Upper 

 Zorritos and the Variegated ; two are common to the Lower 

 Zorritos and the Variegated ; four are common to the Upper 

 and Lower Zorritos, and a number of species from the 

 Lower Zorritos formation have close relatives in the Upper 

 Zorritos. These figures lead to the observation that in point 

 of common species the Variegated faunule is more closely 

 related to the Upper Zorritos than to the Lower Zorritos, 

 but the incompleteness of the Variegated faunule leaves 

 too many possibilities open to permit serious consideration 

 of that. . 



There is, however, apparently a difference in facies be- 



