558 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



datum plane in the case of the Costa Rican beds being an uncon- 

 formably underlying marine shale with invertebrates. Furthermore, 

 the Santa Ana plants are contained in a tuff, and all of the tuffs 

 known to me from the Caribbean to Patagonia are late Tertiary to 

 Recent, and correspond to the great period of vulcanism that started 

 in the late Tertiary. 



This is slender evidence, to be sure, but a considerable body of 

 facts is accumulating to prove the recency of the last and greatest 

 period of orogenesis in the Andes. 



I think that the Venezuelan fossil plants are of approximately the 

 same age as those in the tuffs near Santa Ana, Colombia. Both are 

 undoubtedly Miocene. Those from Venezuela are said to antedate 

 the last great orogenesis of the Cordillera de Merida, which is really 

 nothing but a northeasterly continuation of the Andean Cordillera 

 de Bogota. Moreover, the latest considerable transgression of the 

 Caribbean Sea, represented by the deposits that presumably underlie 

 the whole Maracaibo basin, but are now largely masked by Pleistocene 

 and Recent deposits, except where they are uplifted along the flanks 

 of the mountains, occurred, according to the present conceptions as 

 elaborated by Vaughan 10 during the lower and middle Miocene, or, 

 in terms of European geology, during Burdigalian and Helvetian 

 times. 



Summarizing these statements, the Venezuelan plant-bearing beds 

 represent a series that may be compared with the Gatun formation 

 of the Canal Zone, which has been satisfactorily shown to be of 

 Burdigalian and Helvetian age, although Toula " considered the 

 contained and mixed (in the collecting) fauna as Pliocene. The 

 underlying marine shales are probably Burdigalian or Helvetian, 

 and the fossil plants could therefore be Burdigalian, Helvetian, or 

 younger. From the fact that they antedate the latest extensive 

 orogenesis of the region, which I regard as Pliocene, since conclusive 

 evidence of Pliocene orogenesis is available in the Antilles and 

 elsewhere in this general region, and because the upper Miocene 

 has been demonstrated to have been a time of general uplift, I am 

 inclined to regard the fossil plants as representing the middle Mio- 

 cene, although they may be upper Miocene. They seem to me to 

 be distinctly pre-Piiocene, although it must be admitted that the 

 present collection is far too small to warrant an uncompromising 

 conclusion. It is also realized that our knowledge of this vast 

 region is very limited, so that the present suggestion of age is made 

 with all due reservation. By implication, the same age would be 

 indicated for the plant-bearing tuffs near Santa Ana, Colombia. 



10 Vaughan, T. W., Bull. 103, U. S. Nat. Mus., 1919. 



» Toula, F., Jahrb. k. k. Qeol. Reichanstalt, vol. 5S, pp. 673-760, 190S; vol. 61, pp. 4S7-530, 1911. 



