HILL: GEOLOGY OF JAMxVICA. 203 



almost lost to sight by the overshadowing pre-eminence of the grander 

 and later topographic features that surround them. These may then 

 liave been either islands in the Jurassic sea, the nucleal lands of modem 

 Central America, the fundamental structure of wliich seems to have 

 been since developed on lines parallel to these shadowy ancestors, or the 

 southern margin of the North American continent itself It is possible 

 that during the Jurassic epoch the Caribbean Sea, into which the waters 

 of the Pacific flowed freely from the west, was partially enclosed by an 

 archipelago consisting of a Windward bridge on the east, the old Paleo- 

 zoic ridges of northern Guatemala, and southernmost Mexico, Cuba, 

 and Haiti on the north, and the South American land on the south. 

 Panamic America, together with the submerged Mosquito and allied banks 

 extending northwest to Jamaica, are regions concerning which we can 

 attempt no restoration of their history in Jurassic and early Cretaceous 

 time, as they nowhere exhibit rocks of Pre-Cretaceous age. Neither is 

 it possible t^interpret the history of the Bartlett, Yucatan, and Gulf 

 basins in those days. They may or may not have existed as at present 

 in Jurassic and Cretaceous times. If they did, no data are at hand for 

 prognosticating whether they were connected or disconnected bodies of 

 water or connected with either ocean. The Caribbean, however, most 

 probably, and possibly the Gulf of Mexico, were Pacific indentations at 

 this time. 



It is a well known fact that the close of the Jurassic and beofinninof of 

 the Cretaceous was a revolutionary period in American continental con- 

 figuration. The gigantic Sierra Nevadan uplift, whose southern and 

 eastward extents are not clear, elevated portions of the pre-existing Pacific 

 borders of North America into land. Simultaneously with or just after 

 this event in earliest Cretaceous time, the Atlantic side of the Cordilleran 

 continent in the Mexican region underwent profound subsidence. The 

 Gulf of Mexico was then as now an embayment of the Atlantic Ocean, 

 which began to encroach upon the pre-existing margins of the Appalachian 

 and Cordilleran regions. The interior shore of the Gulf migrated from 

 the eastern part of Texas to southwestern Kansas, and degraded and 

 buried the former southward extension of Appalachian lands then exist- 

 ing in the Coast Plains of northeastern Texas for a distance of 400 miles, 

 while an embayment at its northwest corner near southwestern Kansas, 

 indicated that the arterial Missourian-like drainage at that time was far 

 westward of the present location. The Gulf also made a \vestern trans- 

 gression across Tropical Mexico from at least the present Gulf shore line 

 to the present Pacific coast, and left thick deposits of chalky sediments 



