1890.] NATURAL SCIENCES OF PHILADELPHIA. 445 



THE GEOLOGY AND PALEONTOLOGY OF THE CKETACEOUS 

 DEPOSITS OF MEXICO. 



BY PROFESSOR ANGELO HEILPRIN, 



III the following pages I have attempted to present, so far as they 

 are known to me, all the leading facts touching the geological and 

 paleontological relations of the Cretaceous deposits of Mexico. It 

 is true these are still far from sufficient to permit us to analyze with 

 satisfaction the minor details of the geology of so vast a region as 

 the Mexican Republic, but they serve to clearly mark out its more 

 salient geognostic features, and to establish its relationship with the 

 great continental mass lying to the north and with the oceans which 

 bound it on the east and on the west. My own observations were 

 made in the spring of the present year (1890), when, as chief of the 

 scientific expedition organized under the auspices of the Academy 

 of Natural Sciences of Philadelphia, I traversed much of the 

 south-central region of the Republic, from the Atlantic nearly 

 to the Pacific, at the same time that I enjoyed the opportunity of 

 studying special collections which had been previously made at points 

 not reached by our party. 



The conclusions stated in the present paper are the following : 



1. Cretaceous deposits cover, or are scattered over, the greater 

 part of Mexico, from the Atlantic plains to the Pacific, and from 

 the Rio Grande to (or through) the States of Colima, Michoacan, 

 Guerero and Oaxaca. These deposits are continuous with the Cre- 

 taceous area of the interior basin of the United States, and are 

 largely the equivalents in age of the deposits which are represented 

 in Texas and in the other Gulf States. 



2. The Mexican Cretaceous deposits that have thus far been iden- 

 tified by fossil remains represent a horizon not lower than the Cen- 

 omanian, while the greater bulk of the formation is of Turonian or 

 Senonian age. The deposits are thus a part of the Middle (?) 

 and Upper Cretaceous series of the true geological scale. 



3. No unequivocal deposits of Lower Cretaceous age — as equiv- 

 alents of the Gault, Neocomian, etc. — have yet been discovered in 

 the Republic, although some such may exist intermingled with, or 

 underlying, the newer series. 



4. The great central plateau of Mexico consists in greater part of 

 nuclear Cretaceous strata, over whose uneven summits a more or 



