CORRELATION OF THE JURASSIC 663 



lower latitudes is interesting and suggests an amelioration of climate at 

 the end of the Jurassic and the merging of the climatic zones which 

 were more marked earlier in that period. 



The maximum transgression of the West Indian Jurassic embayment 

 of the Atlantic evidently obtained during the Portlandian, for fossils 

 of that age are found in the easternmost Jurassic outcrops in Cuba, in 

 the Malone Mountains in Texas, 31 and in Mazapil and Durango in 

 Mexico (figure 15.) 



Summary 



The Organ Mountains, in the Province of Pinar del Kio, western 

 Cuba, are composed for the most part of black limestones and shales, 

 weathering brown or white and characterized by layers of fossiliferous 

 concretions (of the accretion type) containing ammonites, pelecypods, 

 gastropods, and, in some localities, fishes and marine reptiles. The 

 formations are thin at the eastern end of the mountains, in the regions 

 north of Candelaria and San Cristobal, where they are about 375 feet 

 thick, but increase westward, attaining their maximum development 

 of upward of a thousand feet in the section between Viiiales and Con- 

 stancia. The westernmost outcrops are seen at Guane. The strata dip 

 down under the Tertiaries, which form the coastal plain bordering the 

 mountains, and reappear in the Isle of Pines to the south. 



The formations range from the Middle through the Upper Jurassic, 

 the existence of the Bajocian, Bathonian, and Callovian at Constancia 

 and La Griiira being somewhat doubtful, because all of the ammonites 

 upon which those older horizons were determined are new species. The 

 presence of rocks of upper Oxfordian, Lusitanian, Kimmeridgian, and 

 upper Portlandian age is indicated by the occurrence of species of am- 

 monites characteristic of those formations in Europe and also of many 

 species which are new but are related to European Neo- Jurassic forms. 

 In the eastern foothills of the Organ Mountains the upper Portlandian 

 is found resting with a basal conglomerate on ancient folded rocks; 

 westward the Kimmeridgian, Lusitanian, Oxfordian, and older Jurassic 

 strata come in successively beneath the Portlandian, the relation being 

 clearly indicative of a marine transgression from west to east, the basal 

 conglomerate becoming younger in age eastward. The eastern shore- 

 line of the embayment of the Jurassic Atlantic, at the period of maxi- 



31 F. W. Cragin : Paleontology of the Malone Jurassic formation of Texas, with strati- 

 graphic notes on Malone Mountain and the surrounding region near Sierra Blanca, Texas, 

 hy T. W. - Stanton. U. S. Geol. Survey Bull. 266, 1905, 109 pp., pis. ii-xxix. 



