CHIAPAS, TABASCO, AND PENINSULA OF YUCATAN 943 



mined as Tertiary. In 1891 I found in the alluvium of the 

 Chixov River Tertiarv species of Ostrca and Cerithhun. 



In 1894 I found Tertiary fossils near Moyos, Sabanilla, Tila 

 and Tumbala ; Ostracc in Tenosique, near Chinaja, in San Anto- 

 nio, department of La Libertad, Chiapas ; near Tenejapa and at 

 other points. Other Tertiary fossils (Lamellibranchs) were 

 found by D. Joaquin Zetina on the banks of the Lacanja River, 

 the Aguilar and other streams, and one Ostrea by D. Jose Tam- 

 borrel in the southern part of Tenosique. 



I found in Real, department of Chilon, and in San Antonio, 

 department of La Libertad, Chiapas, fossil plants in Tertiary ter- 

 raines ; but as they were not in place, I could not determine 

 their age. 



The Tertiaries are generally very much inclined ; in the 

 neighborhood of Istapa, of San Antonio, of Tenejapa and Tum- 

 bala, the strata are horizontal or of very gentle dip ; they are 

 more modern than the andesitic eruptions because they enclose 

 pebbles of the latter, as in Burrero, district of Istapa ; and in 

 some cases the horizontal rocks lie directly above the andesite, 

 as near to Tenejapa. 



In the peninsula of Yucatan Tertiary beds predominate ; and 

 it seems that from the south to the north the successive strata 

 become more and more recent until the Post Pliocene and Qua- 

 ternary^ of the north coast is reached. I think that the nearly 

 horizontal or little inclined Tertiary beds of Yucatan which I 

 have observed, have a general, gentle slope toward the north, 

 and that a great part of the more recent Post Pliocene beds were 

 submerged under the sea in comparatively recent times as Heil- 

 prin concludes was the case with the "Banco de Yucatan," and 

 quite probably the submerging took place very slowly, just as 

 now, according to my own observations, the Atlantic coast of 

 Guatemala is slowly sinking. 



The southern parts of Yucatan show calcareous formations 

 often containing much silicons matter. Among the limy layers, 

 too, are occasional beds of marl and others of gypsum (alabas- 

 ter). In the mountain chain of Ixconconcal, near Icaiche, I 



