420 J. P. Kimball—Geological Relations and Genesis 
the contact, within the area of the still lower syenyte foot-hills, 
and the emerged corallines of the present coast margin. Ye 
such corallines may have once existed, aud since disappeared 
by subaerial erosion. 
Nor is proof afforded of any former extension of the dioryte 
mantle below or south of the contact. Diorytic dykes, never- 
theless, in great number, penetrate the syenyte on every hand, 
their frequency becoming less toward the west, as distance 
increases from the culmination of the Juragua foot-hills. Be- 
yond them, west of the Carpintero, but in line with the 
second range of foot-hills, or just back of the general course of 
the contact, the syenyte hills have been wholly denuded of 
dioryte, the hills themselves becoming gradually degraded 
toward the bay of Santiago, and exhibiting the extreme effects 
of weathering decay characteristic of highly crystalline feld- 
spathic rocks in lower latitudes. Remnants of detritus, dioryte 
and hematite, upon the surface of these hills, attest the former 
extension of at least a thin development of the dioryte mantle. 
Unlike the lower syenyte hills of the Juragua group, these hills 
have not opposed to erosive agencies a great number of ribs 
or dykes of more enduring trappean. roc 
of foot-hills, as recognized by the bodies of hematite and mar- 
ble, are proofs of a sum of uplifts of not less than 1300 feet. 
