GENERAL SUMMARY OF FIELD RELATIONS 653 



long period of uplift and erosion a great part of the Cretaceous cover was 

 stripped off from the elevated central areas. When the island was in 

 whole or in part submerged by the Oligocene sea, sediments were 

 deposited in many places directly upon the eroded Jurassic rocks, as 

 the unconformable contacts indicate. On account of the differential 

 uplift of the western end of the Organ Mountains, the Upper Jurassic 

 rocks have there been worn away, so that only the lower part of the sec- 

 tion is preserved, while eastward the stratigraphically higher, but topo- 

 graphically lower, beds are shown (figure 1-i). But for this differential 

 uplift the Jurassic section would be complete in the latitude of Vihales; 

 and, since strata ranging from the Oxfordian into the Kimmeridgian 

 have been found at Constancia, it is possible that there may even be 

 isolated outcrops of the Portlandian remaining. That such outcrops 

 probably occur is indicated by the presence of the Portlandian species 

 SimbirsTcites mexicanus Burckhardt and Kossmatia zacatecana Burck- 

 hardt in concretions which, according to Dr. Koig's statement, came 

 from sections north of Vinales. 



Correlation of the Jurassic of Cuba and Mexico 



The Jurassic ammonite fauna of Cuba bears a close resemblance to 

 that of Mexico, there being a sufficient number of species in common 

 to make possible a general correlation. Burckhardt, in his two mono- 

 graphs on the Jurassic of Mexico, 18 has made known to us the strati- 

 graphic and faunal succession in San Pedro del Gallo, in the State of 

 Durango, and in Mazapil. In the former region there are some 1,700 

 meters of black shales and limestones ranging from Lower or Middle 

 Jurassic age through the Portlandian and succeeded by Cretaceous strata. 

 The ammonites are found in black, bituminous concretions identical in 

 color and lithological character with those in Cuba. Two hundred and 

 fifty kilometers east of San Pedro del Gallo is the very thin section at 

 Mazapil, where there are less than 100 meters of shales and limestones 

 representing the Kimmeridgian and Portlandian and resting upon a 

 thick series of limestones and marls containing pelecypods, corals, and 

 Nerineas of uncertain age. Faunally, the Cuban Jurassic is more like 

 that of San Pedro del Gallo than that of Mazapil. Both regions contain 

 a certain number of widespread European species which make intercon- 

 tinental correlations possible, but they also show many provincial forms 

 which have no very near relatives in the European fauna, but which are 



18 Carl Burckhardt : La Faune Jurassique de Mazapil. Inst. Geol. Mexico, Boletin No. 

 23, 1906, 216 pp., 43 plates, and Faunes Jurassiques et Cretaciques de San Pedro del 

 Gallo. Inst. Geol. Mex., Boletin No. 29, 1912, 264 pp. and 46 plates. 



