38 Bulletin 30 454 



would expect to meet with successively older outcrops, providing 

 this sequence had not been altered by folding or faulting. That 

 this may take place is shown by the low anticline found between 

 Hato Viejo and Potrero on Rio Amina. So while the geographi- 

 cal sequence is suggestive, we have placed little reliance upon it 

 in the determination of the stratigraphy. But as a matter of 

 fact it has practically coincided with the faunal evidence. 



Evidence of the Mollusca. — In view of the large numbers of 

 species from the various localities and the rarity of what might 

 be taken as index fossils, the method of reciprocal percentages 

 has been used, as already explained, to determine relationships. 

 The results were very significant and may be briefly summarized. 



Resume of Reciprocal Percentages 



Rio Mao at Cercado 



Bluff 1 Bluff 2 Bluff 3 



19.6 to F. 



14. — A. 



10 — B. 1 to 1. 



* * * * * # 



3—3- J 5— 3- 



2— G 



1.5—2, 



Rio Gurabo at Los Quemados. 



Zone A Zone B 



19 to B. 19 to A. 



14 — 1. 10— 1. 



• * * * * * 



i—3- -7—0. 



• 7-G 



• 5-1. 

 4-H. 



1 to I. 



.92— F. 



* * * 



15—2. 



7— Bulla R. 



6—1. 



4-H. 



3-G. 



Zone D 



10 to E. 



2 — 1. 



* * # 



.8— H. 



■7—3- 



.4-1. 



