586 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



It is true that in the south the Hmestones and dolomites are in general of darker-gray to 

 black tones and are thus distinguished from those of the north, which exliibit clear, mostly 

 yellowish color values. The conglomerates often contain interbedded layers which are colored 

 red by iron oxide. The predominance of brighter colors in the limestones of the north does not, 

 however, prevent the frequent occurrence of limestones and especially of dolomites of dark- 

 gray tones in that region; but it has not been possible to show that there was any difference in 

 age between the lighter and darker limestones. 



The paleontological evidences also fail to bring complete satisfaction, for only the light- 

 colored limestones contain fossils, such as the remarkable Barettia, and in other localities 

 Sphserulites or remains of Radiolites, which have not yet been accurately determined. In many 

 places there are organic breccias of mussels and snail shells, which, however, are not accurately 

 determinable. Yet as they occur with well-recognizable traces of Rudistes they evidently 

 belong to the Upper [?] Cretaceous. H I find remains of Rudistes as far south as the crest of 

 the Chicoj Range, but thence southward the limestones and dolomites of the Coban terrane , 

 have failed to yield a trace of fossils. They seem to be older than the Upper Cretaceous lime- 

 stone of the north. The boundaries of the Coban limestone with the Carboniferous limestones 

 and dolomites on the south are as difficult to fix as are those of the Cretaceous in the north, and 

 for that reason they are shown upon the map only by dotted lines. 



Sapper estimates the thickness of the Cretaceous at about 800 meters. 



Bose ^^ in 1905 described at some length the Lower Cretaceous (Eo- and Meso- 

 Cretaceous as he described the beds) of Chiapas and expressed the opinion that the 

 Neo-Cretaceous (Upper Cretaceous) was lacking in that province. He says: 



The Eo-Cretaceous of Chiapas is composed of argillaceous, sandy, slate-colored strata, red 

 beds, slate-colored limestones, and sandstones in thick beds. These strata occur beneath the 

 limestones with Rudistes and in the south in contact with the Todos Santos terrane. The ' 

 limit between the basal Cretaceous and the Todos Santos has not been carefuUy studied. The 

 Lower Cretaceous in the south is everywhere followed by Cretaceous limestones with Rudistes. 

 Moreover, it occurs in the basin of Chiapas, where it is laid bare by erosion. The thickness of 

 this formation is about 300 or 400 meters. It is followed conformably by Cretaceous with 

 Rudistes, as may be seen to the south and west of Tuxtla, Gutierrez, and Chiapa. Sapper 

 classed these beds as Upper Cretaceous and said that they rest upon the limestone with Rudistes. 

 Tliis is not certain. * * * The few fossils wliich I have been able to examine indicate rather an 

 Eo-Cretaceous than a Neo-Cretaceous age. It should be stated that the greater part of the species 

 which Sapper cites are contained in the private collection of the former director of the Institute 

 Geol6gico, which was not accessible to me. I have from those beds only an Isastrsea sp. nov. 

 very like an Isastrsea of the Eo-Cretaceous of San Juan Raya, two examples of Nerineopsis 

 goysuetse Aguilera, n. gen., n. sp., and some poorly preserved corals. It is possible that to this 

 division belong also certain gray and brown strata with masses of limestone which occur near 

 Cancuc, at the northern base of the Mesa Central. * * * It is quite probable that these 

 strata correspond to the upper part of the Metapan terrane, which is found in the southern part 

 of Guatemala, in western Honduras, and in the northwest of San Salvador and which consists 

 also of marls, sandstones, and argillaceous rocks and conf orru ably underlies the limestones 

 with Rudistes. 



Bose then goes on to describe the Cretaceous hmestones with Rudistes ("Meso- 

 Cretaceous") and says: 



This division is much the most important in Chiapas. * * * jj consists of limestones 

 and dolomites which generally occur in quite thick beds and only occasionally as intercalated 



a Probably Meso-Cretaceous of the Mexican Survey or Comanche series of the United States Geological Survey. — 

 T. W. Stanton, comment on manuscript. See also citations from Bose and Aguilera, beyond. 



