HILL: GEOLOGY OF JAMAICA. 203 
almost lost to sight by the overshadowing pre-eminence of the grander 
and later topographic features that surround them. These may then 
have been either islands in the Jurassic sea, the nucleal lands of modern 
Central America, the fundamental structure of which 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 
timo, as they nowhere exhibit rocks of Pre-Cretaceous age. Neither is 
it possible to interpret the history of the Dartlett, 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. 
Tt is a well known fact that the close of the Jurassic and beginning 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 western 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 
